>nal Bureau of Standards

Library, fi.W. Bids

JUN 2 7 1360

NBS MONOGRAPH 16

Vibration-Rotation Structure in Absorption Bands

For the Calibration of Spectrometers

From 2 to 16 Microns

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March 3,

1901, as amended by Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods for making measurements consistent with these standards; the determination of physical constants and

properties of materials; the development of methods and instruments for testing materials, devices,

and structures; advisory services to government agencies on scientific and technical problems; in- vention and development of devices to serve special needs of the Government; and the development

of standard practices, codes, and specifications. The work includes basic and applied research,

development, engineering, instrumentation, testing, evaluation, calibration services, and various

consultation and information services. Research projects are also performed for other government

agencies when the work relates to and supplements the basic program of the Bureau or when the

Bureau's unique competence is required. The scope of activities is suggested by the listing of

divisions and sections on the inside of the back cover.

Publications

The results of the Bureau's work take the form of either actual equipment and devices or published papers. These papers appear either in the Bureau's own series of publications or in the journals

of professional and scientific societies. The Bureau itself publishes three periodicals available from

the Government Printing Office: The Journal of Research, published in four separate sections,

presents complete scientific and technical papers; the Technical News Bulletin presents summary

and preliminary reports on work in progress; and Basic Radio Propagation Predictions provides

data for determining the best frequencies to use for radio communications throughout the world.

There are also five series of nonperiodical publications: Monographs, Applied Mathematics Series,

Handbooks, Miscellaneous Publications, and Technical Notes. Information on the Bureau's publications can be found in NBS Circular 460, Publications of the

National Bureau of Standards ($1.25) and its Supplement ($1.50), available from the Superintendent

of Documents, Government Printing Office, Washington 25, D.C.
UNITED STATES DEPARTMENT OF COMMERCE • Frederick H. Mueller, Secretary NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director

Vibration-Rotation Structure in Absorption

Bands for the Calibration of Spectrometers

From 2 to 16 Microns

Earle K. Plyler, Alfred Danti, L. R. Blaine, and E. D. Tidwell

Reprinted from the Journal of Research of the National Bureau of Standards—A. Physics and Chemistry, Vol. 64A, No. 1, January-February 1960.

National Bureau of Standards Monograph 16

Issued June 21, 1960

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington 25, D.C. - Price 20 cents
Contents

Page

1. Introduction 1 2. Utility of the molecular band method 1 3. Instruments and methods used in calibrating the standard lines 1 3.1. 5 to 16 micron region 2

a. Instrument 2

b. Method of calibration 2

c. Chart reduction 2

d. Instrument and calibration 2

e. Refractive index 3

4. Comments on measuring technique and use of the standard lines 3

5. Discussion of spectrograms 3

5.1. CO2, j<2 fundamental 3

5.2. Acetylene, v5 fundamental .__ 3

5.3. NH3 , v2 fundamental 4

5.4. Methane, fundamental 4

5.5. H2 0, vi fundamental 5

5.6. CO fundamental 7

5.7. C13 02 , vz fundamental . 7

5.8. CI2 0,, V3 band 9

5.9. HBr fundamental 11

5.10. HC1 fundamental 12

5.11. Methane, v3 band 12

5.12. Acetylene bands near 3,300 cm-' 13

5.13. Water and carbon dioxide bands near 3,700 cm-1 13

5.14. C02 , 021, and 101 bands 14

5.15. C2 H2 , v x + v5 band 14

5.16. CO harmonic band 17

5.17. N2 0, 2vx band and hot band 17

5.18. NH3 , Vi fundamental 18

6. Polystyrene film 18

7. Summary 20

S. References 20 n
Vibration-Rotation Structure in Absorption Bands for the

Calibration of Spectrometers From 2 to 16 Microns 1

Earle K. Plyler, Alfred Danti, 2 L. R. Blaine, and E. D. Tidwell

(September 23, 1959)

Suitable bands of common gases have been tabulated and remeasured wherever neces- sary from 2 to 16 microns to obtain an accuracy of about 0.03 cm-1 throughout the region

and to provide good calibrating points at frequent intervals. Some 600 rotation-vibration

lines are illustrated in 20 spectrograms and wavenumbers are listed in companion tables with considerable intercomparison with worthy data obtained in other laboratories. The

absorption bands were remeasured or calibrated by using either a precisely graduated

grating circle or standard atomic lines with the fringe system formed by a Fabry-Perot inter- ferometer. Characteristic features of the individual bands are discussed briefly and refer- ences to other publications are given. The substances used for calibration include H2 0, C02 , CO, HC1, HBr, NH3 , CjHj, CH4 , N2 0, and polystyrene film.

1. Introduction

In recent years, infrared spectroscopists have ex- pressed concern regarding satisfactory methods and

wavelengths for calibrating good prism and small

grating spectrometers [1, 2, 3, 4].

3 In the past, a number of publications [5, 6, 7, 8, 9, 10, 11] from

several laboratories did tend to ease the immediate

requirements ; but with the influx of finer instruments

the need for more thorough, suitable, and precise

coverage has arisen. Professor Mizushima and fellow

workers have clearly indicated in their detailed measurements [12] that the small grating instruments are

certainly capable of producing rather precise data.

The present work addressed itself to the need for bringing together and remeasuring suitable bands of

common gases in order to certify absolute accuracy

to within several hundredths of a cm-1 throughout

the region and to provide calibration points at fre- quent intervals.

2. Utility of the Molecular Band Method

Although in several cases (extremely precise measurements on CO [13, 14, 15] and HCN [16]) the use of

molecular bands for calibration purposes is probably

as good as the use of atomic lines, this method should

not take preference over the use of atomic lines when

precise measurement is being considered. However,

when measurements good to several hundredths of a cm-1 are sufficient or in cases where other limiting

factors enter, viz, broad bands, then this method may

1 This research was supported by the Air Force Cambridge Research Center and by a NASF grant to MIT.

' Guest worker from MIT.

' Figures in brackets indicate the literature references at the end of this paper.

offer a number of advantages. In the case of prism

instruments, the use of appropriate atomic lines for calibration is rather limited to the visible and near

infrared regions and the need for single order coverage

throughout is apparent. Present day commercial in- struments are more easily calibrated in absorption

than in emission and the molecular band method

obviates the need for a full battery of atomic line equipment as well as personnel capable of using it. In addition, only available or easily obtainable substances have been used in this work so that laboratories should experience little difficulty in using this method. Most of the gases are available in typical

chemistry laboratories and it will be mentioned that

work in this laboratory has indicated that, in general,

natural gas from commercial lines and acetylene

drawn from the welder's tank are suitable for cali- bration purposes. Should impurity peaks arise in these bands, use can still be made of the lines which

are clearly those tabulated and illustrated in the

following sections.

Some 600 lines, which provide rather thorough

coverage, are tabulated and illustrated in 20 spectrograms. For certain bands, the number can be appropriately increased by having reference to recom- mended publications given in the discussion section.

Attempts were made to keep the number of different

gases used at a minimum and they include: H20,

C02 , CO, HC1, HBr, NH3 , C2H2 , CH4 , and N20. Also

a polystyrene film has been included.

3. Instruments and Methods Used in

Calibrating the Standard Lines

Two instruments in the Radiometry Section of the

NBS were used in measuring the bands and in the 2- to 4-n region most bands were measured on both in- struments at different resolution and the results compared.

1
3.1. 5 to 16 Micron Region

a. Instrument The previously described [17] grating spectrometer with an off-axis collimating mirror of 1-m focal length was used in conjunction with an extremelyprecise grating circle reported to be accurate to at

least 3 sec of arc for any angle [18]. For the longer wave work (5 to 16 n) the lead telluride detector was

replaced with a thermocouple detector. When this instrument was used in the 2- to 4-/i region, the

thermocouple detector was purposefully used so that

resolution could be lowered and made comparable to that of small grating instruments. A KBr fore- prism arrangement with fixed foreprism slits and a manually adjustable prism was used for order separation throughout this work. Under these stated conditions the instrument was capable of resolving lines separated by 0.3 cm-1 in the 7- to 16-^ region and up

to about 1 cm-1 in the 2.5- to 6.5-^ region.

b. Method of Calibration With a microscope attachment, angles were read

off the inscribed circle, centered with respect to the

spindle of the cone which rotates the grating, and

fiducial marks recorded on the chart. During

measuring runs, readings were taken every 5 min of arc and a slow drive speed (~23 min per deg) was

used. It was found that proper positioning of the

foreprism energy upon the entrance slit of the

spectrometer proper was necessary in the sense that

for extreme settings, where the maximum of energy

being admitted to the spectrometer would come

about 5 grating degrees away from the point of

interest, the frequencies of measured lines would be

in error by several hundredths of a cm-1. By making frequent settings of the foreprism (about every

2 deg of grating angle) so that the energy would be

maximized and hence placed symmetrically on the

entrance slit, these effects could be ignored. Such

considerations were, of course, of greater importance

in regions where wide spectrometer slits were

required or at long wavelengths where the dispersion

of KBr is greatest. (This matter was considered in some detail, since it is felt that it is a frequently over- looked source of error occurring with the use of fore- prisms.) In the course of any complete run (standards plus spectrum to be measured) no changes were made in instrumental conditions (viz, retardation

resulting from changes in amplifier response settings

may shift the line center) unless absolutely necessary.

At the start of the work, it was decided that the

precisely measured CO fundamental lines (see ref. [13]) (table 4) be used as standards wherever possible.

The procedure devised was that of using the simplified grating relation, n\=K sin 0, where an "effec- tive" grating constant, K&lr , incorporating spectrometer characteristics, could be calculated by measuring about 15 CO lines and the physical central image.

This was done with the grating being turned first in one direction then in the reverse direction. If slightly different, the K's obtained separately for each direction would be averaged. Once a good

value of K had been determined for a grating, tbi central image was always calculated from the 10 (o|

so) standard lines recorded either before or immei

diately following a measuring run. Using this pro!

cedure, the frequency of standard CO lines couhj

always be recalculated from chart measurements t- within about ±0.01 cm-1 of the accepted value' 11 With good spectrometer and grating alinement, ii fl was felt that CO standards could be used to calibrat

NH3 , CH4 , and H50 lines even though the gratin 1 angle for the standards differed appreciably froc

that of the lines in question. In calibrating th

lines, both standards and runs to be measured

would be recorded with the grating being turned i] the same direction. As is often the case, it was found

that slightly different values would be obtained fo! the two directions. Final values represented th:

1 average of an equal number of measurements in eaclj fi direction. It is believed that the tabulated value; are accurate to ±0.02 cm-1 in this region.

c. Chart Reduction Wherever possible single lines were picked out fo

jj measuring, but in some instances certain comple:

lines were measured since they are particularly suited : for direct prism observation. It is advisable t

s ]} record spectra on ruled chart paper where the ruled

lines are reproducible perpendicular to the char' ' ] edge. The determined center point of the line to b

11 measured can then be easily projected to a suitabljj 1 measuring base line on the chart by using a pair oi dividers and the nearest ruled line. The center oj

the line should be determined with a pair of stii I dividers at about the 2/3 absorption point and no I at the peak or apparent maximum of absorption. I Ii the spectrum is particularly noisy the center should » be determined at a number of places from the 2/3 to 3/1 point of the maximum of absorption and the averagi i taken. Fractional distances between "pip" mark' 1 should be measured to within 0.005 in. using a steer

f rule and visual enlarger if necessary. For th) t majority of measuring runs, 5 min of grating an I corresponded to 2 in. on the chart.

d. Instrument and Calibration The instrument, which uses the double-pasi j system and is capable of resolving about 0.03 cm"

| has been described [19] and only a few details need > be added. Standard atomic lines and the fring \ system described in a previous paper (see ref. [17); i| were used to calibrate the molecular bands. B;j

^ scanning the spectrum slowly and averaging several runs, a set of relative values for the lines of a bani. I can be determined to a few thousandths of a cm"

' and the absolute to ±0.01 cm"1

. With scanning a : ; a medium rate, absolute values are probably in erro

"

n by ±0.03 cm-1

. The accuracy of measurement o f this instrument is increased by the lines being ver lt narrow (0.03 cm-1

). Measurements made unde,

^ lower resolution (about 1 cm-1

) with the othe L instrument in this region agreed with these to aboui [> ±0.05 cm-1

. This indicates that low resolutioi 7
pectrometers can measure with an error of about

,10 of the resolution.

e. Refractive Index In this laboratory measurements on both instru- ments are carried out with the grating in air so that

imported frequencies were corrected to vacuum by

<ing refractive index tables, and temperature and

pressure corrections given by Penndorf [20].

1

I. Comments on Measuring Technique and

Use of the Standard Lines

For the present-day molecular spectroscopist who

jFjjrisb.es to carry out precise measurements, useful

joints on measurement technique, whether on

jtandard or unknown lines, have already been

3 mentioned in previous sections on method of calibraion, instrument performance, chart reduction, and

lso in reference [17]. Concerning a spectrum to be

measured, in cases where the instrument is being

j sed at or near its resolution limit (ripple spectrum)

, v r in the case of complex lines or shoulders, then the

jj>est possible "center" point must be picked and this

,,

( iay necessarily have to be near the absorption peak

0ince lines may not be well enough developed to thermit measurement at the 2/3 to 3/4 absorption

Joint.

Itl It is advisable to record both spectra and standards for each direction of grating turn if the driving

mechanism is equally accurate in both directions,

fit'rovisions or modifications should be made on comi lercial or laboratory instruments so that the grating

[Ian be used in both directions with near equal

accuracy and the results averaged. Undoubtedly,

- m most laboratories the standards will be used in

yonjunction with reproducible pip marks. Data

;:i rill be extracted from simple pip or drum number

a ersus frequency (cm-1

) relations by fitting a straight

nine to two end points and an extended deviation

njurve plotted. In view of extremely precise data

or certain bands (CO, HCN) the utility of using

hese standard lines in higher orders for the same

rating angle should not be overlooked. In terms

f precision measurement, it would appear that the

§ branch (1,000 to 1,200 cm"1 ) of the v2 NH3 band

"light also be classified in this categoiy. This

: igher order procedure, of course, requires refractive

[fiidex considerations for conversion to vacuum and

( ach spectral region must be handled independently.

>t In making use of the standard lines under lower

t higher resolution, workers should exercise neces- sary care. For example, in the CO bands where

apart from some isotopic overlap) the lines are

; ingle and suitably spaced throughout, even ripple

1 eaks observed with a prism instrument would serve

s satisfactory calibration points. Whereas, in

"T many other bands proper usage under lower resolution may require judicious use of sufficiently low

pressures and slow scanning speeds to assure the

i! roper development of lines and eliminate "pulling"

y strong neighboring absorption.

5. Discussion of Spectrograms

In general, the runs made on white chart paper for

illustration purposes were made at somewhat faster speeds and with much more chart concentration

than was the case for the measuring runs. On some

of the illustrations, sloping or bowing backgrounds

are due either to foreprism effects or the joining of

separate sections.

5.1. C02 , v2 Fundamental

Some 20 lines in this band were remeasured and

comparison is made with the work of Rossman, Rao,

and Nielsen [21-A, 21-B] and also with the values

reported by Mizushima et al. (see ref . [12]) . Although

our measurements were somewhat handicapped by

the overly strong absorption (7-m path) and also by

poorer grating resolution in this region, the agreement is quite good. It appears that the values re- ported by Rossman, Rao, and Nielsen (also additional unpublished work communicated by Dr. Rao)

are accurate and that lines they report both at higher

and lower frequency as well as those given in table 1 may be used for calibration purposes provided the

atmospheric absorption is augmented by C02 used in a vapor cell. The spectrum is illustrated in figure 1.

Table 1. Absorption lines of fundamental of CO2 from 685

to 700 cm-*-

R(J) P(J)

Rossman, Mizushi- Rossman, Mizushi- J Rao, and Thiswork ma et al.*> Rao, and Thiswork ma et al.k Nielsen » v cm-1 v cm-1 Nielsen • v cm-1

v cm-'

v em-1 (vac.) (vac.) u cm-1 (vac.) (vac.)

(vac.) observed observed (vac.) observed observed observed observed

2 669. 75 665. 83

4 71.34 .28 64. 28

6 72.88 .88 .87 62. 71 8 74. 45 .46 .43 61. 18 .15 .15

10.... 76.02 .06 .02 59.64 .55 .60

12 77.60 .59 58.08 .06 .09

14 79. 20 .16 56. 55 .51 .53

16 80. 78 .76 55. 02 4.98

.48

.00

18 82. 36 .39 .35 53. 48 .47 20 83. 95 .98 .95 51.95 .91 .94

22 85. 55 .56 .55 50.41 .39 .41 24 87. 16 .17 .14 48. 90 .89

26 88. 77 .79 .78 47. 39 .38

28 90. 38 .36 .36 45.90 .89 .87 30 91. 99 .97 .99 44. 37 .39

32 93. 59 .60 42.86 .88

34 95. 19 .20 41.35 .40 .38

36 96. 82 .82 39.83 .90

38 98. 44 .42 38. 34 .35

40 700. 07 .04 .89

.68

36.87

42 01.69 35. 38 .40 Q Branch.. » (10°0H>01'0) 720. 46

a Rossman, Rao, and Nielsen [21].

•> Mizushima et al. [12].

0 The measuring point of this band was taken at the 2/3 absorption point.

5.2. Acetylene, vb Fundamental

This band was included in order to provide useful

calibration points between the end of the strong 15-ju

C02 band and the ammonia band. On the low3
WAVE NUMBER, cm

Figure 1. The v2 fundamental of CO2 recorded in the first order of an 1,800 lines/in. grating under atmospheric conditions and 7-m -path.

Spectral slit width about 0.5 cm"1.

frequency end, our values are in excellent agreement with the recently published values of Rao,

Ryan, and Nielsen [22] and table 2 includes additional values as reported by these authors. At

higher frequency, results are also compared with the

work of Christensen, Eaton, Green, and Thompson

[23]. The agreement is quite good except between

lines 29 to 39, where several lines appear to be pulled

out of position by an overlapping band. These lines are set out by parentheses. Results of recent measurements by Jones and Nadeau of the National

Research Council, Ottawa, Canada are also included.

The spectrogram is illustrated in figure 2.

5.3. NH3 , v2 Fundamental

Table 3 gives values obtained in four different

laboratories for this band. Since these four works

are of about equal quality, the average value re- ported in the last column represents a simple numerical average (within arbitrary ±0.04-cm-1 exclusion conditions). The average values are probably

better than individual determinations, and it is estimated that they are good to within ±0.01 -cm

-1 absolute on the average. The region from 1,000 to 1,200 cm-1

is particularly good. We have cause for suspicioning some of our low-frequency lines (numbers 1,3, and 6) due to the fact that the grating was

being used at exceedingly high angle. As more

experimental and theoretical data become available

for ammonia, a good set of calculated values may

ultimately replace the average value column. The

spectrum is shown in figure 3.

5.4. Methane, vt Fundamental

This band serves the purpose of providing connection between the ammonia and water bands and is included mainly because workers with small instruments may have difficulty in observing weak water

lines in this region. We are unable to compare these

Table 2. Absorption lines of vs fundamental of acetylene fro 680 to 790 cm'1

Line serial number

This work

' cm-> (vac.) observed

698. 53

703. 28

1 (05. 66)

07. 96

10.30

12. 68

15. 08

16. 36

17. 35

19.90 (peak)

(22. 15)

24. 39

36.17

38. 56

40. 89

43. 29

45. 64

47. 97

50. 36

52. 66

(55. 12) 57.42

(59. 85)

62. 11

(64. 46) 66.74

69.08

71.39

73. 71

(76. 02) 78.42

(80. 70) 83.07

85. 43

87.75

90. 10

Rao, Ryan,

and Nielsen » v cm-1 (vac.) observed

686. 77

89. 11 91.47 93.80

98. 19

98. 52

700. 89

03. 24 05.60

07. 96

10.30

C, E., G., and T t> v cm-1 (vac.) observed

698. 50

700. 88

03. 19

05. 56

07. 94

10. 37

12. 67

15. 03

17. 35

19. 90

22. 06

24. 35

36. 18

38. 56

40.88

43.31 45.64

48.02

50. 37

52.74

55. 14

57. 45

59. 86

62. 18

64.52

66. 87

69.21 71.53 73.84

76. 17

78. 52

80. 82

83. 09

85. 45

87.74

90. 12

Jones and Nadeau » v cm-' (vac observed

89.

91. 93

96,

98. 700.

03.

05.

07.

10

12.

15.

0 Rao, Ryan, and Nielsen [22].

•> Christensen, Eaton, Green, and Thompson [23].

0 Jones and Nadeau, National Research Council, Ottawa, Canada, imp

lished work.

d Parentheses around values in second column indicate poorer lines.

4
WAVE NUMBER, cm 700

1 720 740

1

1 760

1 1 780

1

C2 H

2

34 38 \

6 8

10 12 V i

19 V » v D 30

16 1 26 42 C02 C

2 H

2

-

Figure 2. The v$ fundamental of acetylene recorded in the first order of an 1,800 lines/in. grating with 8-cm pressure and 5-cm path.

Spectral slit width about 0.7 cm-

'. The low frequency end of the P branch overlaps with atmospheric absorption of CO2 and the strong Q branch (hot band) of CO2 at 720.46 cm-1 also contributes to absorption at this point.

3. Absorption lines of fundamental of NH3 from

760 to 1,210 cm-1

This work

v cm-i (vac.) observed

760.72 70.96

78. 33 91.76

96.17

809. 76

14. 27 30.68

34. 86

51.36

52. 77

67. 83 (blend)

71.77

72.59

92. 06 (blend)

908.21 18.65

35. 85 (poor) 48.25

51.83

61.01 (poor)

71.91

91.71

92. 60 (blend)

1,007. 55 11.20 27.04

32.14

46.41

53.14

65.58 70.60

74.17

84. 61

89. 38

95. 15

1, 103. 44

10.67 16.02

22.15

31.85 36.78

40.62

47.53

52.86 58.93

77.09

95.02

1,212.66

Garing and

Nielsen • ccm-' (vac.) observed

.69

.91 .29

.72

.14

.72

.25

.65

.82 .32

.71

(. 53. . 74, . 93) .73

.56

(1. 88,.17 .62

.90

.22

.06

Price and

coworkers b v cm-1 (vac.) observed

Mizushima

et al. c vcm-1 (vac.) observed

.69

.90 .27

.76

.16

.71 .22

.70

.84 .36

(. 53, . 73, . 96) .74

.58 8.02

.14) (1. .14)

(.45,.68

,70)

.54 .20 .04

.13

.40

.13 .57

.59

.14

.60

.42

.15

.46

.69

.03

.76

.65 .52

.86

.98

.08

.00 .68

.15

.61

.25

(0. 89, . 12) .92

.71

(.46, .71)

.56 .22

.04

.13

.42

.14

.55

.59 .17

.62

.39

.16 .42

.69

.03

.75

.65

.54

.87 .95

.10

4. 99

.69

.90

.64

.48

.24 6.92

.12 .27

.14 .46

.53

.13

.56

.31

. 15 .44

.67 5.97

.10

Average

value d

v cm-'

(vac.)

.34

.74

.82

.76

.58

.99

.08

.18 .63

.88

.25

.70 .62

.55

.22

. HI .13

.41

.14

.57

.59

.15

.61

.40

.15

.44

.68 .03

.14

.87 .76

.64 .53

.95 .09

5.00

"T » Garing, Xielsen, and Rao [24].

I b Price and coworkers [33].

1 c Mizushima et al. [12]. M d Numerical average of the 4 determinations. If a number differed by 0.04 or more from the average of the other 3, it was excluded frorn the average.

numbers with others, as there are no other precision

measurements available but our results (see table

4) would appear to be good to about ±0.02-cm-1 absolute. The spectrum is shown in figure 4.

5.5. H2 0, v-2 Fundamental

Some 50 good lines of varying intensity were picked

out for measurement. (See table 5.) Wherever possible, the lines are compared with recent precision

determinations of Rao, Ryan, and Nielsen (see ref.

[22]). These authors indicate that their values are, on the average, about 0.07-cm-1 lower than those

reported by Dalby and Nielsen [25] for the region

1,450 to 1,650 cm-1

. Our results, when compared

with Dalby and Nielsen's values, would indicate

that this is the case throughout the band. Wherever

possible, mild flushing or pumping down of the spectrometer housing is to be recommended for cleaner

development of the lines but our results indicate

that good calibration measurements can be made

even on saturated lines provided the line is not a complex one. This band is illustrated in figure 5.

Table 4. Substructure of v4 band of CH4 from 1,200 to 1,370

Serial This work number v cm-1 (vac.) observed

1 1, 216. 26

2 30.12

3 33. 47

4 41.01

5 47. 81

6 56.60

7 65.52

8 75.20

9 81.59

10 92. 61

11 97.63

12 1,311.42 13 22.09

14 27.20

15 32. 41

16 41.79

17 46.70

18 53. 06

19 66. 04

5
Figure 3. The v% fundamental of NH3 recorded in the first order of a 3,600 lines/in. grating with 7-cm pressure near the bar

center and 12-cm for the wings, both with 5-cm path.

Spectral slit width about 0.3 cm-'.

WAVE NUMBER, Cm-i

1380 1340 1300 1260 1220

Figure 4. The vt fundamental of CH4 recorded in the first order of a 3,600 lines/in. grating with 12-cm pressure and 5-cm pat)

Spectral slit width about 0.5 cm-'. The open circles refer to atmospheric water peaks.
"able 5. Absorption lines of v2 fundamental of HoO from

1,300 to 2,000 cm.-1

Line

serial lumber

78

9

10

1112

13

1415

16

171819

20

2122

23

24

25

This work

v cm-i (vac.) observed

1,312. 55

18.92 36.68

54.83

61.08

68.62

75. 07 94.46

1, 404. 99

17.42

29.94

47. 93 52.04

64.92 81.25

87.29

98. 80

1,512. 30

28. 57

b (45. 09)

64.93

94.52

96. 29 1,601.25 09.46

Rao, Ryan, and Nielsen ! v cm-1 (vac.) observed

64. 91

64. 91

94. 51

96. 27 01.23

Line

serial number

26

27

28

29

30

313233

3435

36

37

38

39

40

4142

43

4445

46

4748

49

50

This work

i cm-1 (vac.) observed

16. 77 27.88

37. 53

40. 31 62.82

71.49

90.15

1,704. 49

10. 23

23. 49

56. 81 68.17

75.64

84. 95

i> (90. 94)

99.60

1, 810. 63 25.24

47. 80

69. 35

89.59

95.19

1, 918. 05 42.60

88. 43

<> (2, 016. 79)

Rao, Ryan,

and Nielsen < v cm-' (vac.) observed

« Rao, Ryan, and Nielsen [22]. b These lines are less accurate.

5.6. CO Fundamental

The CO fundamental band at 4.67 m was measured

accurately by Plyler, Blaine, and Connor (see ref. [13])

in 1955. With the measurement of the CO harmonic

(2.33 p), it was possible to calculate the position of

the fundamental band. This has been done by Rank

and his colleagues (see ref. [14]) and a very good agree- ment with the observed values was obtained. There was a slight difference in values for the high J's in

the R branch. Recently the R branch has been re- measured and a better correspondence with the cal- culated values is obtained. The accuracy of the

calculated values approaches a few thousandths of a cm-1

. The spectrum is shown in figure 6 and the

values are listed in table 6.

5.7. C13 02 , v3 Fundamental

The C

1302 band is excellent for calibration from

2,240 to 2,280 cm-1 and connects with the v3 band of C

1202 . This spectrum was measured in 1955 by

Plyler, Blaine, and Tidwell [26]. In this work, the

lines of this band have been remeasured and the

values check closely with the first determination.

Unfortunately, the J values were incorrectly listed in table 1 of the above publication and each J of the

P branch should be reduced by 2 ; that is, P 44 should

WAVE NUMBER , cm ~

~~l

1 1620 1540 1460 1380

H

2 0

lA1

24 I fun

2000 1920

l r 1840 1760 1680

Figure 5. The v2 fundamental of H2 0 recorded with a 3,600 lines/in. grating under atmospheric conditions (T=21° C, humidity

21%) and 7-m path. The upper spectrogram was recorded in the first order and the lower in the second order. Spectral slit width about 0.6 to 0.7 cm-i for both spectrograms.

\ble 6. Absorption lines of CO from 2,020 to 2,240 cm-1

jumper

D 28

2726

25

I 24

23

22

2120

19

18

I 17

1615

14

1312

11109

Plyler, Blaine, and

Connor a v cm-1 (vac.) observed

2, 022. 899 27.635

32.349

37. 030

41. 663

46.271

55. 391

59. 911

8.851

77. 650

82. 009

86. 322

90.603

94. 870

99. 096

, 103. 265

07. 413

11. 555

19. 677

23. 700

31. 639

35. 554

39. 432

Rank et

al. b v cm-1 (vac.) calculated

.915

.650

.354

.026

.278

.402 .916

.849

.652

.005

.324

.611

.865 .085

.272

.426

.546

.684

.702

.635 .549

.429

Line number

i?0

12

3

4

2, 154. 596

58. 309

Plyler, Blaine, and

Connor 1

v cm-1 (vac.) observed

65. 602

72. 759

76. 287

79. 761

83.226

86. 636

90. 010

93. 357

96. 661

99. 929

2, 203. 147

06. 345

09. 498

12. 600

15. 685

18. 733 21.732 "21.750

24.694 24.712

27. 638

30. 526

33. 362

36. 186

38. 958

Rank et

al. b v cm-1 (vac.) calculated

.598

.302

.761 .286

.774

.226

.641 .020

.361 .665

.933

. 163 .355

.510

.626

.705

.746

.749 .713

* Plyler, Blaine, and Connor [13].

>> Rank et al. [14].

c New measurements agreeing more closely with calculated values.

>e P 42, etc. The work with a small grating spec- rometer of Mizushima and his colleagues (see ref. 12]) has also been included and there is very good

greement between the two lists of frequencies. The

pectrum of this band is shown in figure 7-A and the

alues are listed in table 7-A.

5.8. C

120,. v3 Band

The only precision work for this band is the work

vhich was done at the NBS. The frequencies were

iLTst published in 1955 (see ref. [26]) and since then

iwo other determinations have been made. With

he long paths employed in this laboratory, it is not

Table 7-A. Absorption lines of v?, fundamental of C'HV'

from 2,240 to 2,300 cmr1

p

- P r»

' This work IV! izu- This ous'~ IvT izu- Line work v Plyler, shima et Line work v work shima et Blaine, al this lab- al b ai. ber (vac.) and Tid- cm-' ber (vac.) oratory c v cm-' observed well a (vac.) observed v cm-1 (vac.)

*',cm . observed (vac.) observed

t, vac; observed observed P 40 2 247. 68 2 247. 66 R 0 2 284. 24 38 49. 68 . 68 2 85. 79 . 76 . 83 36 51. 70 . 67 4 87. 31 33 34 34 53. 66 g 88. 81 . 80 . 83

32 55. 59 g 90. 23 . 20 . 29

10 91. 62 . 62 . 73

30 57. 52 . 52 2 257. 48 12 93! 10 . 12 28 59. 41 . 42 . 40 14 94 45 . 46

26 61. 29 . 30 . 35 16 95. 89 . 91 24 63. 13 . 14 . 30 18 97. 18 . i0 . 26

22 64. 95 .96 5. 04 20 98. 50 .57

22 99. 76 .74

20 66. 75 . 76 . 85 24 2, 301. 05 . 06

18 68. 54 . 55 . 65

16 70. 29 . 31 . 37

14 72. 03 ------- -

12 73! 73 . /4 . 16

108 75.42

77. 09 .08 .03

6 78.71 .71 .64 4 80. 33 .31 .18

2 81. 94

* Plyler, Blaine, and Tidwell [26]. h Mizushima et al. [12].

c E. K. Plyler and L. R Blaine, unpublished work.

possible to measure the central part of the band.

Figure 7-B shows how use can be made of the entire

band by purging the instrument housing and containing the C02 in a cell. (Dr. Norman Jones of

the National Research Council of Canada has furnished the spectogram as observed with a purged

small grating instrument.) Table 7-B gives observed values for the band wings and calculated

values for the central part. In view of the fact

that molecular constants calculated from the observed lines agree well with those of Courtoy [27] obtained from many bands and agreement with observed lines is good, it is felt that workers can use

either the observed or calculated values of table

7-B equally well provided the intensity and resolution of the band is close to that of figure 7-B. Both

WAVE NUMBER ,cm-> 2300 2280 2260

Figure 7-A. The v3 fundamental of C13 02 16 recorded in the iirst order of a 7,500 lines/in. grating under atmospheric conditions and

6-m path.

Spectral slit width about 0.3 cm-'.

9
Figuee 7-B. The v 3 fundamental of C12 02 16 recorded in the third order of a 70 lines/mm grating with a small grating instrument The spectrometer housing was purged of atmospheric CO2 with dry nitrogen and the spectrum recorded with 30-mm CO2 in a 10-cm cell. Spectral slit width abou

0.25 cm-'.

Figure 8-A.

Spectral slit width

Absorption band of HBr recorded in the second order of a 5,000 lines/in. grating with 40-cm pressure and 5-cm path

about 0.8 cm-i. The CO? band just appears at the low frequency end and the HC1 band at the high frequency side. HC1 was present in th HBr as an impurity.

WAVE NUMBER, cm

Figure 8-B. A section of the HBr n - 81 bands with HC1 35

, 37 overlapping.

Recorded with a 10,000 lines/in. grating singly passed with 2.5-mm pressure of each acid in a 6-m cell. Spectral slit width about 0.06 cm-'.

' 0

lii

10
able 7-B. Absorption lines of n fundamental of C12 0216 from 2,280 cm-1 to 2,390 cm-1

Line lumber

P68

66

64

62

60

585654

52

50

4846

R 3032

3436

38

40

4244

46

This work

v cm-'

(vac.) observed

2. 282. 21

86.93 89.23

93. 81 96.03 98.30

2. 300. 50

Previous work this laboratory » * cm-1 (vac.1 observed

2. 293. 81

96. 03

2, 302. 70

04.84

06.96

2, 370. 36 71.48

72.65

73. 71 74.79

75.83

76.87

77.88

Line number

i?48

50

52

54

56

5860

62

64

66

90

This work

v cm-1 (vac.) observed

2, 383. 39

84.22

85. 01 85.80

86. 55

Previous work this laboratory »

v cm-1 (vac.) observed

2. 379. 80 80.74 81.65

82. 51 83.38

84. 21

85. 01

85. 79

86. 55

87. 26

87. 97 88.64

89.32

89.91 90.49

91.10

91.61

92. 16

93.09

93. 55

93. 96

Calculated values for lines near band center

P44

42

4038

2, 309. 05

11.13

13. 19

15. 22

17.23

19.21 21.17

23.11 25.02

26.91

28. 77 30.60

32.41 34.20

35.97

37.71

39. 43

41. 12

42. 78 44.42

46.04

47.63

i?0

2

46

2, 349. 97 51.50

53. 01 54.49

55.95

57.38

58. 78

60. 16

61. 52 62.86

64. 16 65.44

66. 70 67.93

69. 13

E. K. Plyler and L. R. Blaine, unpublished work.

Observed and calculated values should be good to .bout ±0.02-cm_1 absolute. Since the band conists of a collection of no less than four overlapped

)ands, results are subject to being extremely resolu-

•ion sensitive and workers should not use lines exhibting pronounced overlap. (The R branch is comparatively free of such difficulties.)

5.9. HBr Fundamental

As shown in figures 8-A and 8-B, this band was

neasured under considerably different resolution.

vVith the conditions describing figure 8-A, there was

10 evidence to the effect that the components arising

Tom HBr79 and HBr81 were being resolved out. This was done intentionally to see whether, when

measured as a single peak, the frequency agreed with

:he average determined for each component under

resolution approaching 0.05 cm-1

. The low resolution single-peak frequency agreed with the high reso- lution average value to within 0.05 cm-1 on the

average (See table 8). This relatively good agreement does indicate that the high resolution results are correct in the absolute sense and that apart from

greater inability to determine the center of the single

Table 8. Absorption lines of HBr79 anal HBr81 together with

single unresolved peaks at lower resolution (2,390-2,750

cm.-1 )

Serial number

Br" Br"

Br" Br"

Br" Br"

Br" Br"

Br" Br"

Br" Br"

Br" Br"

Br" Br"

Br" Br"

Br" Br"

Br"

Br»

Br" Br"

Br" Br"

Br"

16

17

18

19

20

21

22

23

Br"

Br" Br"

Br" Br"

Br" Br"

Br" Br"

Br" Br"

Br" Br"

Br" Br"

Br" Br"

Br" Br"

Br" Br"

This work high

resolution isoto- pic components

v cm-' (vac.) observed

2, 392. 61

92.94

2, 412. 73

13.06 32.43

32. 77 51.73

52.08

70. 61

70.97

89. 43

2, 507. 11

07. 48

24.71

25. 08

41.87

42. 25 74.80

75. 19

90.56

90. 95

2, 605. 82

06. 22

20. 63

21.03

34. 92

35. 33

48.71

49. 13

61.99

62. 39

74. 76

75. 19 87.00

87.41

99.11

2, 709. 86

10. 29

20. 48

20.89

30. 51

30. 95

40. 02

40. 4fi 48. 93

49. 39

High

resolution average

2, 392. 78

2, 412. 89

32.60

51.91

70. 79

89.26

2, 507. 30

24. 90

42. 06

74. 99

90. 76

2, 606. 02

20.83

35. 13

48. 92

62. 19

74. 97

87.20

98.90

2, 710. 07

20. 68

30. 73

40.24

49. 16

This work low

resolution

single peak

v cm-' (vac.) observed

2, 412. 93

32. 65

51.94

70.82

89.30

2, 507. 24

24.83

41. 99

74. 98

90.67

2, 605. 95

20.81

35.03

48.85

62. 13

u
peak (near 1-cm-1 half-width), its frequency is given

well enough by the component average. In table 8, the high resolution average of components is the

recommended value for single peak use. Calculated

values were also determined for the high resolution

results and the values given in the first column of table 8 are believed to be accurate to within ±0.02-

cm_1 absolute.

5.10. HC1 Fundamental

The spectrum illustrated in figure 9 was recorded

under low resolution and the entire band shown in

this way for the sake of compression. Figure 8-B

shows 3 lines of the band under high resolution.

The band was measured on both instruments in this laboratory and results are compared with values

reported by Mills, Thompson, and Williams [28] (see table 9). Molecular constants were obtained

from the high resolution observations and calculated

line frequencies agree well with the observed. In

general, the high resolution results of this work fall between the low resolution values and those of Mills, Thompson, and Williams. The high resolution work does not, however, represent precision

measurement, since the lines were measured at medium-fast scan in order to appropriately cover

this extremely wide band in reasonable time. The

observed values given in the table for the high

resolution work are to be preferred and represent

the best possible set. These values should be good

to about ±0.02-cm _1 absolute. (Future precision

measurements are contemplated for this band.)

5.11. Methane, v3 Band

The E branch of this band and some of the lower

lines of the P branch are fairly suitable for providing

calibration points in this region. However, care should be exercised to the extent of staying within the

bounds of the resolution illustrated in figure 10.

Table 9. Absorption lines of HC1 from 2,650 to 3,050 cmr

Serial number

This work high

resolution v cm-1 (vac.) observed

This work high

resolution v cm-' (vac.) calculated

This work low

resolution v cm-' (vac.) observed

M.,T.,and W.

v cm-i (vac.) observed

HC1"

0-

1.- 2

i." 4..

5.. 6-

7_. 8..

9..

10-

11- 12. 13.

14.

15.

16.

17. 18.

0__ 1-

2..

3..

4_.

5..

6..

7..

8.. 9..

10.

11.

12.

13. 14.

IS. 16.

17.

18.

2, 651.98 2, 651. 98

77. 74 .75 .86

2, 703. 02 2, 703. 02 . 03

27. 79 .79 . 76

52. 05 .05 . 15

75. 77 .77 .85

98. 95 .95 .96

2, 821. 58 2, 821. 57 .56

43. 63 .63 . 60

65. 10 .10 .14

2, 906. 25 2, 906. 25 .24

25. 91 .90 .89 44.92 .92

63. 30 .30 .20

81. 02 .02

98. 07 .07

3, 014. 44 3, 014. 44

30. 10 . 11 .12 45.07 .08 .02

HC1"

2, 650. 23 2. 650. 24

75. 96 .96

2, 701. 20 2. 701. 19 .28

25. 93 .93 .95

50. 14 . 14

73. 84 .83 .89

96. 98 .98

2, 819. 57 2, 819. 57

41. 59 .59

63. 02 .03

2, 904. 12 2, 904. 12 .14

23. 74 .74 .79 42.74 .73 .66

61. 08 .08 .06

78. 77 .77

95. 79 .79

3, 012. 15 3,012. 14 . 14

27. 80 .79 .72

42. 74 .74 .68

Mills, Thompson, and Williams [28].

WAVE NUMBER, cm-'

Figure 9. Absorption band of HC1 recorded in the second order of a 5,000 lines/in. grating with 20-cm pressure and 5-cm path

Spectral slit width about 1.0 cm-1

. Weak atmospheric water lines of the 2i<2 band begin to appear at the high frequency end. 12
3.448

WAVELENGTH , fj. 3.333

2900 3000

WAVE NUMBER, cm-i

3100

Figure 10. The v-i fundamental of methane recorded with a 7,500 lines/in. grating with 10-cm pressure and 5-cm path.

Spectral slit width about 0.9 cm-', certain weak lines occurring between methane lines are part of the 2^ band of atmospheric water vapor.

Jnder higher resolution the lines begin to break up,

jSP 4, for example, shows four components within 0.37

ju

_1 and frequency allocation becomes difficult. ifPhe values are listed in table 10 and strongest components should be used where indicated.

5.12. Acetylene Bands Near 3,300 cm-1

I • • 1 The spectrogram of figure 11 gives a rather inter- - sting comparison of lines and peaks under considerably differing resolution. The scale on the lower

'"able 10. Absorption lines of methane from 2,900 to 3,170

Line number

Plyler, Blaine, and Nowak » cm-i (vac.) observed

Line number

Plyler, Blaine, and Nowak » v cm-

' (vac.) observed

P12 i> 2, 895. 18 R0 3, 028. 84

11 k 2, 906. 72 1 38.58

10 i> 16. 36 2 48. 25

9 26. 86 3 57. 79 8 37. 34 4 67.30

7 47.92 5 76.74

6 58.20 6 86. 02

5 68.67 7 95. 22

4 79.00 8 3, 104. 30

3 88. 27 9 13.42

2 99. 10 10 22.46

11 31. 39

12 40.20

13 48. 95

14 57. 61 15 66. 20

Plyler, Blaine, and Nowak [11]. Frequency of strongest component.

panel, though close to that of the upper one differs somewhat and is indicated by the tie lines. The

values listed in table 11 indicate the rather re- markable feature that even under considerably lower

resolution single or symmetrical lines can still be

accurately measured. The high resolution measure- ments were made with fringes and the grating circle was used for the lower resolution measurements.

In two cases (lines 6 and 7; 20 and 21), two closely

spaced and nearly equal intensity components were measured as a single peak and this value compared

with the average of the two components. As in the

case of HBr, the agreement is quite satisfactory.

The results of this work are compared with values

reported by Christensen, Eaton, Green, and Thompson (see ref. [23]).

5.13. Water and Carbon Dioxide Bands Near 3,700

cm-1

The spectrogram (fig. 12-A), illustrating the

atmospheric absorption in this region, was recorded

with the low resolution instrument so that results

would approximate those attainable with small

grating intruments. The indicated lines were measured under these conditions and in table 12-A the

results are compared with the high resolution and

high precision work of Plyler and Tidwell [29]. The agreement is satisfactory and indicates that even with lower resolution, good measurements in the order of 1 part in 100,000 can still be made. The

higher resolution numbers are the recommended

ones and if more frequent calibrating points are

required, workers should make use of reference [29].

13
WAVE NUMBER , cm -1

3 34 0 3 310 3 28 0 3 25 0 3220

C2 H

2

Figure 11. The two absorption bands of acetylene near 3,800 cmr1 compared under high and lower resolution. The upper spectrogram was recorded with a 10,000 lines/in. grating singly passed with 1.5-cm pressure and 5-cm path. The lower spectrogram was recorded in tt second order of a 5,000 lines/in. grating with 4-cm pressure and 5-cm path. Spectral slit widths about 0.10 and 0.8 cm-i, respectively. Atmospheric water lini of the 2»

2 band are denoted by open circles.

5.14. C02, 021, and 101 Bands

Plyler and Tidwell (see ref. [29]) report the precis

measurement of many of these lines. Certain others

which could not be measured due to overlappin

water lines, are not listed in table 12-B. Most o these lines are good to about ±0.02 cm-1

. The tW' bands are illustrated in figure 12-B as recorded wit. a nitrogen-purged small grating instrument witi CO2 in a cell. (The spectrogram was recorded b; Dr. Norman Jones, National Research Council

Ottawa, Canada.)

5.15. C2H2 , vy-\-v5 Band

From the end of the P branch of the CO harmoni

to the beginning of the v3 water vapor band there i a gap of about 100 cm-1

. There is a band of acety

lene of medium intensity that falls in this regio:

(4,039 to 4,130 cm"" 1 ). This band is overlapped b; four weaker bands and when measured with Ioa pressure and high resolution many lines are observe

[30]. When a pressure of 1 atm is used in a 10-cr

cell, the smaller bands are not observed and thj P and R branches of the band stand out clearly. 1 number of the strong lines were measured unde

both high and low pressures and the values agree

closely. The numbers listed in table 13 are th) results of the low pressure measurements. Th

spectrum is shown in figure 13.

14

Table 11. Absorption bands of aceii/lene {2 bands) from 3,200

to 3,380 cm-1

Serial number

This work

medium-high

resolution » cm-'

(vac.) observed

This work low resolution

v cm-1 (vac.) observed

C, E„ O., and T b medium

resolution v cm-' (vac.) observed

(H2 0)

'48.38

3, 219. 42

25. 63 30.72

38. 31

48. 19

48. 56 50.71 55.59

60. 46

65. 29

70. 10

78.22

83. 04

86. 63 95.88

3, 300. 46

07. 27

17. 92

22.41

22. 77

31.29

35.59 39.83

44.08

48. 23

55.74 (H2 0)

65.78 (H2 0)

67.67 (H2 0)

»22.59

.44

.41

. 82 (slightly blended)

. 60 (slightly blended)

.32

. 01 (slightly blended)

.21

.64

.72

. 29

!34 » 48.40

.47 .65

.56

.40 .26

.04

.20 2.93

.48 .83

.35

. 14 .99

22.44

. 18 .49

.72

3. 93

0 Average of two components of nearly equal intensity.

b Christensen, Eaton, Green, and Thompson [23].
WAVE NUMBER, cm-i

H

2 0

3600 3500 3400

|igube 12-A. Atmospheric absorption bands of H2 0 and CO2 in the 3,700-cmr1 reqion recorded under intermediate resolution in

the second order of a 5,000 lines/in. grating. The path was 7 m with 48 percent humidity at 23° C. Spectral slit width about 0.7 cm-'.

able 12-A. Absorption lines of water from 3,400 to 4,000

Line serial number

(8) 9

1010-A(CO2) 111213

14

1515-A

16

17

18

1920

2122

High resolution Plyler and Tidwell

vcm-i (vac.) observed

3. 397. 20

3.447.20 (7.03) 96.63

3, 518. 97

(2 components)

70. .54 76. 89

77.23

3, 603. 08

77.06 avg

59.94

98.00

~3.~714."81

3, 883. 26

3, 920. 10

53.11

69.15

90.72

4, 008. 59 44.90

Intermediate resolu- tion this work

v cm-i (vac.) observed

3. 447. 21

96. 62

3, 519. 05 36.44 avg

57. 21

70.48

77.02 avg

3,602.98 (complex)

38.15

59.94

98. 08

3, 701. 90

3, 714. 82 79.38

3, 835. 06

80.52

83. 32

3, 920. 28

42. 86 53.22

69.16

90.74

4, 008. 59

Plyler and Tidwell [29].

Table 12-B. Some precisely measured C02 lines of the 021 and 101 bands at 3,609 and 3,716 cm.'1

Plyler and Plvler and

Line Tidwell » Line Tidwell * number v cm-1 (vac.) number v cm-1 (vac.) observed observed

021 Band

P38 3, 579. 34 R2 (3, 615. 25) 36 81.31 10 (21. 17) 32 85. 21 12 22. 50 26 90.78 14 23. 93 24 92. 65 16 25. 27

22 94. 42 26 31.85

20 (96. 22) 40 40.00

16 99. 74

14 3, 601. 40

10 04. 81

8 06. 48

6 08.07

101 Band

P36 3, 682. 78 R 6 3, 720. 09 32 86.74 10 22. 90

26 92. 46 12 24. 35

24 94. 34 14 (25. 72) 20 98. 00 IS 28. 42

18 99.79 20 29.73

14 3,703. 29 22 31.01

12 05. 02 26 33. 48

10 06.70

8 08. 38

» Plyler and Tidwell [29]. Values in parentheses indicate lines which may be overlapped by water lines.

15
WAVE NUMBER, cm

Figure 12-B. The 021 and 101 bands of C02 recorded with a purged small grating instrument. The C02 was contained in a 10-cm cell at 25-cm pressure for both bands. Spectral slit width about 0.30 cm-'.

WAVE NUMBER, cm

-1

Spectral slit width about 0.08 cm-'. [| |j 18
iBLE 13. Absorption lines of acetylene from 4,040 to 4, ISO cm~l

Line number

Previous work

this laboratory

v cm-i (vac.) observed

Line number

Previous work

this laboratory

f em-1 (vac.) observed

P3 4, 084. 14 RY1 4, 130. 10

11 64.58 15 26. 91

IS 54.52 13 22.63

17 49. 36 11 18.30

21 38.95 9 13.94

7 09.47

5 04.98

3 4, 100. 47

1 4, 095. 84

5.16. CO Harmonic Band

The CO harmonic band at 2.34 p. has been measred very accurately by Rank and his colleagues

see ref. [14]) and also by Plyler, Allen, and Tidwell

;ee ref. [15]). This band is one of the few which

ave been measured in the infrared to such a preci-

.on that the reported frequencies are accurate to a ;w thousandths of a cm-1

. This spectrum was

leasured with a 60-cm ceU and 20-cm pressure, but

10-cm cell with 50-cm pressure is sufficient for

bserving forty lines of this band. The spectrum is hown in figure 14 and the frequencies are listed in

able 14.

Table 14. Absorption lines of the 2-0 harmonic band of CO

from 4,100 to 4,340 cm'1

Line number

P 2726

25

24

23

22

2120

19

18

1716

15

1413

12

1110

Plvler, Allen, and Tidwell

i' cm-1 (vae.) observed

4. 132. 19

37. 79

43. 33

48. 817

54. 234

59. 564

64. 852

70. 066

75. 212

80. 286

85. 302

90. 234

95. 120

99. 931

4. 204. 673

09. 356

13. 962

18. 504

22. 974

27. 371

31. 694

35. 952

40. 150

44. 278

48. 330

52. 308

56. 226

Rank et al. b

i> cm-1 (vac.) observed

.770

.058

.204 .285

.298

.242

954

.1185

. 2117

.307

Line number

R 0

12

34

56

7

Plyler, Allen, and Tidwell > v em-' (vac.) observed

4, 263. 842

67. 548

71. 182

74. 750

78. 235

81. 655

85. 013

88. 298

91.512

94. 639

97. 703

4, 300. 712

03. 614

06. 482

09. 262

11. 969

14. 606

17. 173 19.665

22. 085

24. 425

26. 699

28. 878

31. 022

33. 057

Rank et al.b

v cm-' (vac.) observed

.838

.542

. 179 .743 .234

.661 .010

.290

. 500

.257

.962 .597

.161 .650

.065

.054

4, 335. 030

36. 934

38. 763

40. 517

42. 202

a Plyler, Allen, and Tidwell [15].

t> Rank et al. [14].

WAVE NUMBER, Cm -I

23040 23220 23400 23580 23760 23940

WAVELENGTH, A Figure 14. The 2-0 band of CO recorded with a 15,000 lines/in. grating with 20-cm pressure and 60-cm path.

Spectral slit width about 0.15 cm-'.

24120

5.17. N20, 2f, Band and Hot Band

The 2vx band of N20 has been measured in the

region from 2,520 to 2,580 cm-1 and the results are shown in figure 15 and table 15. Thompson and

Williams [31] had previously measured this band and

their values are used to compare with the results obtained in this work. The lines which have been

measured are noted by a dot on the spectrogram.

There is an overlapping structure of weak lines and

only those lines were measured which appeared in

the open. This band can be resolved by a small

grating instrument if a photoconducting cell is used

as the detector and could be used as an alternate

for HBr in this region. Also there are several regions

where lines are closely grouped and the band can be

used to check instrumental performance and resolution. The measurements of Thompson and Williams

agree, on the average, to within ±0.04 cm-1 of the

17
Figure 15. The 2vi band (2564 cmr1) of N2 0 together with the hot band (2vi + v2 —p2 , 2577 cm~l ) recorded with a 10,000 lines grating with 2-mtn pressure and 6-m path.

Spectral slit width about 0.08 cm-'. The dots denote the measured and tabulated lines.

Table 15. Absorption lines of N2 0 from 2,520 to 2,580 cm'

Thompson and J This work Williams a

v cm-1 (vac.) v cm-1 (vac.) observed obs. laboratory

P45 2, 519. 01 .05

43 21.27 .29

41 23. 50 .52

39 25. 71 .72

37 27.87 .88

35 30. 03 .03 33 32. 15 .17

31 34. 25 .27

29 36.31 .35

27 38. 37 .41

25 40. 38 .42

23 42. 38 .42

21 44. 34 .38

19 46. 27 .32

17 48.19 .23

15 50.07 .13

13 51.92 2.01 (1.97calc.) R 0 2, 564. 18 .24

7 69. 82 .86

11 72.87 .94

13 74. 38 .45

16 76. 56 .59

18 77. 99 8.04

a Thompson and Williams [31].

values in this work. There is a small shift in the

direction of lower frequency of all the values of the

present measurements. An average of the two sets of values would probably be correct to ±0.03 cm-1

, which should be entirely adequate for calibrating

medium resolution instruments.

5.18. NH3 , v4 Fundamental

This band is being included as an alternate to the 6-/u water band and should prove of some use to workers who wish to flush their instruments or use double-beam operation to study samples contained

in cells. Dr. W. S. Benedict, of the Johns Hopkins

University, has picked out of the band (in accordanc

with the resolution illustrated in fig. 16) some 1 single or not-too-complex absorption peaks and ha

determined the best possible frequencies from th

higher resolution results of Garing and Nielsen (sej ref. [24]) and unpublished results from the National

Bureau of Standards Laboratory. The results o

these two works agree to within about ±0.02 cm-1 The frequency assigned to certain absorption peak

which appear single in figure 16 but which actualb

consist of several components is, of course, no longei

applicable if the peak is broken up into its com

ponents under slightly higher resolution. (Th

letter S in figure 16 indicates a single line.) N<

table accompanies this spectrogram but instead tbi

acceptable values which are probably good to ±0.0

cm-1 for single lines and off by as much as ±0.2

cm-1 for some complex lines, have been printed or the illustration. For calibration purposes, the

water lines (see table 5) are considerably better thar

the lines of this band. (The spectrogram waf; recorded by Dr. Norman Jones, National Kesearct

Council, Ottawa, Canada.)

6. Polystyrene Film

In 1950 Plyler and Peters (see ref. [7]) measured

the infrared absorption spectrum of polystyrene on a grating instrument and certain bands were sug- gested for use in calibrating prism instruments

Since that time, films of polystyrene have beer

widely used in many laboratories and it has beer

found very useful in checking the calibration of an instrument in certain regions to ascertain if there are any changes in the reading of the wavelength

or frequency scale of the instrument. There is a question as to the suitability of polystyrene for a calibrating material as it is not completely stable

and has a different absorption spectrum when it>

18
i

iyo I6p0

17,80 17,00 WAVE NUMBER ,cm-l

Figure 16. The vi band of NH3 at 1628 cm-1 recorded with a nitrogen-purged small grating instrument.

Certain strong lines of the n water band still appear. A gas pressure of 7.5 cm in a 10-cm cell was used. Spectral slit width about 0.50 cm-i.

ges. Also different batches of the material may

Jiow differences in absorption. The variation in

7 ie absorption spectrum of different films can

asily be demonstrated, but the strong bands are

Ijijpt appreciably changed in wavelength by age or me origin of the film. In this work, we checked a jm which had been made ten years ago and it aowed no appreciable shifts in the absorption bands,

jfight bands from 6 to 14.4 /x have been remeasured

Tjnd the results are compared with the previous

Measurements of 1950 and the additional measurements of Plyler, Blaine, and Nowak (see ref. [11]) in

! 957. The spectrum is shown in figure 17 and the

,,'avelengths and wave numbers in vacuum are listed a table 16. When the faces of the film are paraUel,

iterference fringes appear but these usually occur

Table 16. Polystyrene absorption bands

Previous measurement

wavelength

(air) fi

New measure- ment this work wavelength (air)

This work

cm-' (vac.)

3. 3026

3. 422

3. 507

5. 138

5. 343

5. 549

6. 238 6. 2427

6. 3151

1, 601. 4s

1, 583. Os 6.692

8. 4615

8. 6626

9. 3524

9. 7226

11. 028

14. 316

1, 181.5o

1, 154. 0|

1, 068.

9

6 1, 028. 2e 906. 5o 698.

3

3

8. 662

9.724

11. 035

100

80

ss0 60

to

to1 40

2

<

rrK

20

0

POLYSTYRENE

5 6 7 8 9 WAVELENGTH, /J. 'igure 17. Infrared absorption spectrum, from 2 to 15 n, of a 50-n film of polystyrene recorded with a rock-salt prism instrument.
between 4 and 6 n for a 50-/z film and do not change

the position of the bands beyond 6/x- The small

band at 6.3151 n, which is on the long wavelength

side of the strong band at 6.24 /i, is completely

resolved by a low resolution grating instrument and

is not overlapped by atmospheric water lines. It should be useful for calibration in this region. The

strong band at 14.316 ju was measured with a film

of 8-n thickness and with this film the maximum

of absorption could be accurately determined. It is estimated that the bands listed in table 16 are accurate to ±0.3 cm-1 and should be useful in

calibrating low resolution instruments, but should

not be considered as being of the same order of

accuracy as the molecular vapor bands. In measuring the polystyrene bands, the center was determined

near the %-absorption point for symmetrical bands

and reference should be made to this point when

making use of the numbers in table 16.

7. Summary

The rather "popular" ammonia band at 3 n was

not used in this work because of its resolution

sensitiveness and also because of temperature and

pressure effects. For example, there are 12 components in the P 8 "line" extending over 1.5 cm-1

. Under low resolution (see ref. [11]) the Q branch,

which extends over 5.5 cm-1 and consists of hundreds

of lines is probably good to 0.5 cm-1. The 16-ju coverage may be appropriately extended

by making use of frequency values reported by

Lakshmi, Rao, and Nielsen [32] for N2O. In this work, we have checked Rao's measurements on the

15-m CO2 band and feel that if the same techniques were used on the N 20 measurements, then these

numbers may be used. Considering the lower

resolution used by the Japanese workers (see ref. [12]) on this band, the agreement with values reported in [32] above is quite good.

At the high frequency end, we have already given

reference to the work of Rank and coworkers on HCN (see ref. [16]) and wish to include also the

grating work on H20 vapor at 1.9 /x and on CH4 at

2.2 m as given in reference [8]. The calibrating values given in this report should

make it easier for infrared spectroscopists to obtain

accurate measurements in the region from 2 to 16 n. As further measurements are carried out in other

laboratories, there will be more values for intercomparison and it should be possible to obtain

calculated values for certain bands which would be more accurate than the observed values from any

one laboratory. No recommended frequencies repre- senting properly weighted averages of the work of

several laboratories have been given, but this may

be done at a later date when more data are available.

It is hoped that spectroscopists will send new data

of this type to the authors for wavelength standards

so that it may be incorporated in a future report.

It is also requested that any corrections or suggested

changes be communicated to the authors.

8. References

[1] R. C. Lord and T. K. McCubbin, Jr., J. Opt. Soc. A

45, 441 (1955).

[2] R. C. Lord and T. K. McCubbin, Jr., J. Opt. Soc. A

47, 689 (1957).

[3] E. K. Plvler and N. Acquista, J. Research NBS t 149 (1956) RP2660.

[4] E. K. Plvler and L. R. Blaine, J. Research NBS ( 55 (1958) RP2821.

[5] R. A. Oetjen, Chao-Lou Kao, and H. M. Randall, R(

Sci. Instr. 13, 515 (1942).

[6] D. S. McKinney and R. A. Friedel, J. Opt. Soc. A

38, 222 (1948).

[7] E. K. Plyler and C. W. Peters, J. Research NBS 4 462 (1950) RP2159.

[8] E. K. Plyler, N. M. Gailar, and T. A. Wiggins,

Research NBS 48, 221 (1952) RP2309.

[9] N. Acquista and E. K. Plyler, J. Research NBS 4 13 (1952) RP2338.

[10] A. R. Downie, M. C. Magoon, T. Purcell, and

Crawford, J. Opt. Soc. Am. 43, 941 (1953).

[11] E. K. Plyler, L. R. Blaine, and M. Nowak, J. Resear NBS 58, 195 (1957) RP2752.

[12] S. Mizushima and colleagues, Tokyo TJniversil Hongo, Tokyo, Japan. A report on the Perki Elmer grating spectrophotometer model 112-

English translation by Perkin-Elmer Corp., Ni

walk, Conn.

[13] E. K. Plyler, L. R. Blaine and W. S. Connor, J. 0]

Soc. Am. 45, 102 (1955).

[14] D. H. Rank, A. H. Guenther, G. D. Saksena, J. Shearer, and T. A. Wiggins, J. Opt. Soc. Am. 4 686 (1957).

[15] E. K. Plyler, H. C. Allen, Jr., and E. D. Tidwell,

Research NBS 61, 53 (1958) RP2883.

[16] D. H. Rank, A. H. Guenther, J. N. Shearer, and T. Wiggins, J. Opt. Soc. Am. 47, 148 (1957).

[17] E. K. Plyler, L. R. Blaine, and E. D. Tidwell, J. J

search NBS 55, 279 (1955) RP2630.

[18] This extremely precise circle was ruled and calibrat by Mr. Benjamin Page of this Bureau.

[19] E. K. Plyler and L. R. Blaine, J. Research NBS ( 7 (1959) RP2922.

[20] R. Penndorf, J. Opt. Soc. Am. 47, 176 (1957). [21-A] K. Rossman, K. N. Rao, and H. H. Nielsen, J. Che: Phys. 24, 103 (1956). [21-B] K. Rossman, W. L. France, K. N. Rao, and H. . Nielsen, J. Chem. Phys. 24, 1007 (1956).

[22] K. N. Rao, L. R. Ryan, and H. H. Nielsen, J. O]

Soc. Am. 49, 216 (1959).

[23] M. T. Christensen, D. R. Eaton, B. A. Green, and : W. Thompson, Proc. Roy. Soc. 238, 15 (1956).

[24] J. S. Garing, Dissertation Abstracts 18, 839 (195

Ann Arbor, Mich. (Abstracts of some U.S. thes issued commercially. This work may appear in future issue of J. Mol. Spectroscopy.)

[25] F. W. Dalby and H. H. Nielsen, J. Chem. Phys. 2 934 (1956).

[26] E. K. Plyler, L. R. Blaine, and E. D. Tidwell, J. H

search NBS 55, 183 (1955) RP2617.

[27] C. P. Courtoy, Can. J. Phys. 35, 608 (1957).

[28] I. M. Mills, H. W. Thompson, and R. L. Willian Proc. Roy. Soc. 218, 29 (1953).

[29] E. K. Plyler and E. D. Tidwell, Extrait des Memori

in 8 de la Societe Royale des Sciences de Lie Quatrieme Serie Tome XVIII, 426 (1956).

[30] H. C. Allen, Jr., E. D. Tidwell, and E. K. Plyler,

Research NBS 57, 213 (1956) RP2711.

[31] H. W. Thompson and R. L. Williams, Proc. Roy. S< 220, 435 (1953).

[32] K. Lakshmi, K. N. Rao, and H. H. Nielsen, J. Che: Phvs. 24, 811 (1956).

[33] H. M. Mould, W. C. Price, and G. R. Wilkinsc Spectrochim. Acta, in press (June 1959).

Washington, D.C.

20 U.S. GOVERNMENT PRINTING OFFICE ; I960
iAAA

THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its major laboratories in Washington, D.C., and

Boulder, Colorado, is suggested in the following listing of the divisions and sections engaged in technical work.

In general, each section carries out specialized research, development, and engineering in the field indicated by

its title. A brief description of the activities, and of the resultant publications, appears on the inside of the front

cover. WASHINGTON, D.C.

Electricity and Electronics. Resistance and Reactance. Electron Devices. Electrical Instruments. Magnetic Measurements. Dielectrics. Engineering Electronics. Electronic Instrumentation. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Optical Instruments. Photographic Technology.

Length. Engineering Metrology.

Heat. Temperature Physics. Thermodynamics. Cryogenic Physics. Rheology. Molecular Kinetics. Free

Radicals Research.

Atomic Physics. Spectroscopy. Radiometry. Mass Spectrometry. Solid State Physics. Electron Physics.

Atomic Physics.

Radiation physics. Neutron Physics. Radiation Theory. Radioactivity. X-ray. High Energy Radiation.

Nucleonic Instrumentation. Radiological Equipment.

Chemistry. Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry. Inorganic

Chemistry. Electrodeposition. Molecular Structure and Properties of Gases. Physical Chemistry. Thermochemistry. Spectrochemistry. Pure Substances.

Mechanics. Sound. Mechanical Instruments. Fluid Mechanics. Engineering Mechanics. Mass and Scale. Capacity, Density, and Fluid Meters. Combustion Controls.

Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Poly- mer Structure. Plastics. Dental Research.

MetaUurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion. Metal

Physics.

Mineral Products. Engineering Ceramics. Glass. Refractories. Enameled Metals. Constitution and Microstructure. Building Technology. Structural Engineering. Fire Protection. Air Conditioning, Heating, and Refrigeration. Floor, Roof, and Wall Coverings. Codes and Safety Standards. Heat Transfer. Concreting Materials.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics.

Data Processing Systems. SEAC Engineering Group. Components and Techniques. Digital Circuitry.

Digital Systems. Analog Systems. Applications Engineering.

• Office of Basic Instrumentation. • Office of Weights and Measures.

BOULDER, COLORADO

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Gas Liquefaction. Radio Propagation Physics. Upper Atmosphere Research. Ionosphere Research. Regular Prediction

Services. Sun-Earth Relationships. VHF Research. Radio Warning Services. Airglow and Aurora. Radio

Astronomy and Arctic Propagation.

Radio Propagation Engineering. Data Reduction Instrumentation. Radio Noise. Tropospheric Measurements. Tropospheric Analysis. Propagation-Terrain Effects. Radio-Meteorology. Lower Atmosphere Physics.

Radio Standards. High-Frequency Electrical Standards. Radio Broadcast Service. Radio and Microwave

Materials. Atomic Frequency and Time Standards. Electronic Calibration Center. Microwave Circuit

Standards.

Radio Communication and Systems. Low Frequency and Very Low Frequency Research. High Fre- quency and Very High Frequency Research. Modulation Systems. Antenna Research. Navigation Systems.

Systems Analysis. Field Operations.
i

j,I