JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. D21, 4668, doi:10.1029/2003JD003709, 2003

Quantum yield for N(4S) production in the ultraviolet photolysisof N2O
Tomoki Nakayama, Kenshi Takahashi, and Yutaka Matsumi
Solar-Terrestrial Environment Laboratory and Graduate School of Science, Nagoya University, Nagoya, Japan

Nori Taniguchi and Sachiko Hayashida
Faculty of Science, Nara Women’s University, Nara, Japan
Received 22 April 2003; revised 27 July 2003; accepted 6 August 2003; published 7 November 2003.

[1] Direct detection of N(4S) atom formation in the 193 nm photolysis of N2O by atechnique of vacuum ultraviolet (vuv) laser-induced fluorescence spectroscopy has beenreported. Tunable vuv laser radiation around 120.071 nm that is resonant to the onephoton N(2p23s 4P1/2  2p3 4S3/2) transition has been generated by two-photon resonant
four-wave sum frequency mixing in Hg vapor. The quantum yield value for N(4S)
formation in the N2O photolysis at 193 nm has been determined to be 2.1 (±0.9)  103.
The N(4S) detection technique, which is developed in this study, is very sensitive, andthe minimum detection limit is estimated to be 2  109 atoms cm3. Impact of thephotolytic N(4S) and NO(X2) production from N2O photolysis on stratosphericchemistry has been explored using a one-dimensional photochemical model, while thefragmentation was not considered in former model calculations. When the N(4S) + NO
dissociation channel is considered in the photochemical model, an enhancement of theNOx production rate (up to 3%) is observed, which is followed by a decrease of the steadystate O3 concentration throughout the stratosphere.
INDEX TERMS: 0317 AtmosphericComposition and Structure: Chemical kinetic and photochemical properties; 0340 Atmospheric Composition
and Structure: Middle atmosphere—composition and chemistry; 0341 Atmospheric Composition and
Structure: Middle atmosphere—constituent transport and chemistry (3334); KEYWORDS: N2O photolysis, NOx
production, stratosphere
Citation: Nakayama, T., K. Takahashi, Y. Matsumi, N. Taniguchi, and S. Hayashida, Quantum yield for N(4S) production in theultraviolet photolysis of N2O, J. Geophys. Res., 108(D21), 4668, doi:10.1029/2003JD003709, 2003.

1. Introduction[2] Nitrous oxide, N2O, is an important atmosphericminor constituent as the main source of odd nitrogen(nitrogen compounds other than N2) in the stratosphere.
Not only do these nitrogen species catalytically destroy O3
directly, but they also control the relative contributions of
the ClOx and HOx cycles in the O3 destruction in thestratosphere [Brasseur et al., 1999]. Most of the N2Otransported through the planetary boundary layer and thefree troposphere to the stratosphere is photolyzed at UV
wavelengths to O(1D) + N2, while a small fraction of N2O
reacts with O(1D) atoms.

N2 O þ hn ! N2 þ O 1 D

N2 O þ O 1 D ! 2NOl  341 nm

ð1Þ

k2a ¼ 6:7  1011 cm3 molecule1 s1
ð2aÞ

! N2 þ O2 ;where the wavelength indicates the thermochemical threshold for channel (1), while k2a and k2b are the rate constantsfor reactions (2a) and (2b), respectively [Sander et al.,2003].
[3] The N2O photolysis around 200 nm has been considered to proceed through channel (1) with an almost unity
quantum yield [Okabe, 1978] and the other energeticallyavailable channels are very minor:

k2b ¼ 4:9  1011 cm3 molecule1 s1ð2bÞ

Copyright 2003 by the American Geophysical Union.
0148-0227/03/2003JD003709$09.00

ACH



N2 O þ hn ! N 4 S þ NO X2  l  248 nm

ð10 Þ


! N2 þ O 3 P l  742 nm

ð100 Þ

! N2 þ O 1 S l  211 nm

ð1000 ÞFelder et al. [1991] studied the dissociation dynamics ofN2O at 193 nm by photofragments translational spectroscopy and reported that channel (10) was unimportant as thetime-of-flight signal intensity at m/e = 30 was less than thedetection limit. Greenblatt and Ravishankara [1990]
reported the upper limit value of the quantum yield forchannel (10) in the 193 nm photolysis of N2O to be 8  103through the chemiluminescent detection of NO products.

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NAKAYAMA ET AL.: N(4S) PRODUCTION FROM N2O

Recently, Adams et al. [2001] detected the N(4S) formationin the 207 nm photolysis of N2O by means of two-photon
absorption laser-induced fluorescence technique (TALIF)
using the same focused laser beam at 207 nm. They havenot measured the quantum yield for N(4S) formation. It isdifficult to estimate the yield from the experiments using a
one-color focused laser beam for both photolysis andprobe.
[4] Although the oxidation of N2O by O(1D), channel (2a),is thought to be the dominant global source of NO in thestratosphere, the photodissociation reaction is a majorremoval process of stratospheric N2O and the O(1D) reaction
is minor as stratospheric sink of N2O. A simple calculation
can predict that a quantum yield of 1% for channel (10) in N2O
photolysis would represent an approximate increase of 15%
in the active nitrogen production rate in the upper stratosphere. Therefore a precise determination of the channel (10)quantum yield is essential for evaluating the stratospheric NO
production rate.
[5] In this study, laboratory studies on the N(4S) atom
formation from the photolysis of N2O at 193 nm has been
carried out using a technique of laser-induced fluorescencein the vacuum ultraviolet region (vuv-LIF). The quantum
yield for N(4S) atom formation from N2O photolysis at
193 nm is determined to be 2.1 (±0.9)  103. The
atmospheric significance of channel (10) as a new sourceof NO in the stratosphere has also been examined with a
one-dimensional dynamical-photochemical model.

2. Experiment[6] The experimental setup used in this study is similar tothat in our previous studies [Matsumi et al., 1994; Hitsuda
et al., 2001], and therefore only brief description is given
here. The unpolarized output of an ArF excimer laser(Lambda Physik, COMPex 102) was employed as a photolysis laser to dissociate the N2O parent molecules. The
N(4S) atoms produced from N2O photolysis at 193 nm wereprobed by the vuv-LIF method at 120.071 nm, which isresonant with the electronic transition of N(2p23s 4P1/2
2p3 4S3/2). The probe vuv laser radiation was generated by
two-photon resonant four-wave sum frequency mixing(wvuv = 2w1 + w2) in Hg vapor around 120.1 nm [Hilbig
and Wallenstein, 1983]. Two dye lasers (Lambda Physik,
Scanmate 2E and FL3002E) were simultaneously pumped
by a XeCl excimer laser (Lambda Physik, COMPex 201).
One dye laser operating with Rhodamine 101 dye in
CH 3 OH solvent generated 4 – 5 mJ pulse 1 around
625 nm. The visible output was frequency doubled in a
KD*P crystal to obtain 312.76 nm (in air), which is twophoton resonant with the Hg electronic transition (6s7s 1S0
6s2 1S0). The other dye laser operating with Coumarin
307 dye in CH3OH solvent produced 2 – 4 mJ pulse1
around 517 nm. The two laser beams were carefully overlapped using a dichroic mirror and focused into the Hgvapor cell with a fused silica lens ( f = 250 mm). The
temperature in the Hg vapor cell was controlled around450470 K to obtain enough vuv probe laser power forexperiments, which corresponds to the equilibrium Hgvapor pressure of 8 – 14 Torr [Smith and Alford, 1987]. Kr
was added in the Hg vapor cell for phase matching and the
optimum partial pressure was 6 – 8 Torr. The generated vuv

laser light was introduced into a photolysis chamber througha LiF window that was used to separate the Hg vapor celland the photolysis chamber. A fraction of the incident vuv
light passed through the photolysis chamber was reflectedby a thin LiF plate held in the end of the photolysis chamberand led into a nitric oxide (NO) photoionization cell. The
relative intensity of vuv laser light was monitored bymeasuring the photoionization current. Typical NO gas
pressure was 2– 3 Torr.
[7] The vuv laser line width was estimated to be
0.28 cm1 full width at half maximum (FWHM) with aGaussian shape. The vuv laser line width was estimatedfrom the shape of the Doppler profile of thermalized
Cl(2P1/2) atom, in which the Cl atoms were produced
from HCl photolysis at 193 nm and were detected at120.135 nm. The necessary vuv laser was generated withthe same experimental setup as used for N atom detection.
The Doppler profile was measured, when 2 Torr of Ar wasadded and the time delay between the photolysis andprobe laser pulses was 20 ms. Under the experimental
conditions, the translational energy of Cl atom is completely thermalized. The repetition rate of the photolysis
and probe laser pulses was 10 Hz. The time delay between
the photolysis and probe laser pulses was controlled by adigital delay generator (Stanford Research Systems,
DG535). The typical time delay for N2O photolysis experiments was 130 ns with a time jitter less than 20 ns.
[8] The vuv-LIF signals from the N(4S) atoms weredetected using a solar blind photomultiplier tube (PMT)(EMR, 542J-09-17). The PMT has an MgF2 window and a
KBr photocathode that is sensitive only between 115 and165 nm. The observation direction of the LIF was perpendicular to both vuv probe and photolysis laser light, andperpendicular to the electric vector of the vuv probe laser.
The output of the photomultiplier was preamplified andaveraged over 10 laser pulses by a gated integrator (Stanford Research Systems, SR-250), and then stored on a
personal computer.
[9] The photolysis chamber was made of stainless steel
with the size 80  80  80 mm, and was continuously
evacuated by a rotary pump (330 L min1) through a liquid
N2 trap. The total gas pressure in the chamber was measured
by means of a Baratron gauge (MKS, 122A, 2 Torr fullscale). N2O (>99.9%) was supplied into the reaction chamber through a needle valve. The typical pressure of N2O was
500– 900 mTorr. While scanning the vuv laser wavelengthfor N(4S) atom detections, the reactants pressure was kept
constant. It should be noted that the high sensitivity of the
vuv-LIF technique makes it possible to detect N(4S) atoms
at low gas pressures and short pump probe delay time(150 ns), and that chemical losses through secondary
reactions, for example, N + N2O, N + NO and N + O2,
can be safely ignored.
[10] In the titration experiments to calibrate the absolutesensitivity of the vuv-LIF system, N(4S) atoms were generated by the microwave (2450 MHz) discharge of pure N2
gas (>99.9%) in a flow tube (Pyrex, 13.7 mm i.d.). A
coaxial flow tube was connected between the N2 discharge
flow tube and the vuv-LIF chamber. NO/Ar gas mixture(0.0268% of NO in Ar) was introduced through the innerinjection tube (Pyrex, 3.8 mm i.d.), which can move along
the outer flow tube. The gas flows were controlled by mass

NAKAYAMA ET AL.: N(4S) PRODUCTION FROM N2O

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flow controllers. All experiments in the present study were
performed at room temperature.

3. Results[11] Figure 1 shows the fluorescence excitation spectrum
for N(4S) atoms produced in the 193 nm photolysis of N2O.
4S3/2) transition
The atomic line profiles of the N(4P1/2
were directly observed by the vuv-LIF method around120.071 nm. The dependence of the LIF signal intensity
for the N(4S) atoms on the photolysis laser pulse is shownin Figure 2. We also checked that no N(4S) atoms signal
was detected without 193 nm photolysis light. These results
indicate that multiphoton absorption processes at 193 nm or
dissociation of parent molecules by the probe laser beams(wvuv, w1, and w2) are safely ignored in this work. The
quantum yield for N(4S) formation from N2O at 193 nm
photolysis was determined by calibrating the sensitivity ofthe vuv-LIF system. The two methods were used toestimate the absolute sensitivity of the detection system
for N(4S) by the vuv-LIF method. One is the titration
technique for the N(4S) atom concentration using chemical
reaction with NO. The other is the comparison between the
LIF intensities of the N(4S) atoms produced in the N2O
photolysis at 193 nm and Cl(2P1/2) atoms produced in the
HCl photolysis at 193 nm. The Cl(2P1/2) quantum yieldfrom the photolysis of HCl at 193 nm has already beenreported [Zhang et al., 1997].
3.1. Chemical Titration Method[12] The conventional titration technique for N atoms wasused to calibrate the vuv-LIF system for detecting N(4S)
atoms [Boisse-Laporte et al., 1997]. The N(4S) atoms weregenerated in a microwave (MW) discharge of pure N2 gas
and were then introduced into the vuv-LIF chamber throughthe coaxial flow tube. While monitoring the vuv-LIF signal

Figure 1. Fluorescence excitation spectra of N(4S)
produced from the photolysis of N2O at 193 nm. The
horizontal scale indicates the wave number shift from the4
S3/2 transition forresonance line center of the 4P1/2
N atom at 120.071 nm. The delay time between thephotolysis and probe laser pulses was 130 ns. The pressureof N2O was 700 mTorr.

Figure 2. Plots of the LIF signal intensity of N(4S) at
120.071 nm versus the photolysis laser power.
of N(4S) atoms at 120.071 nm, NO molecules diluted with
Ar were injected into the flow system. The N(4S) atoms
were consumed by the following reaction:
N 4 S þ NO ! N2 þ O

k3298 ¼ 3:0  1011 cm3 molecule1 s1ð3Þ

where k3298 is the rate constant for reaction (3) at 298 K[Sander et al., 2003]. By monitoring the vuv-LIF signal
intensities as a function of the number density of NO
molecules added, the sensitivity of the vuv-LIF system for
N atom detection was calibrated. A typical titration plot isshown in Figure 3, in which the mass flow rate of NO/Ar
mixture was varied between 0.6 and 2.3 sccm while the total
flow rate was kept constant (19 sccm). When all the Natoms produced by the MW discharge are consumed byreaction (3), the NO concentration corresponds to the initial
N atom concentration. Thus the absolute concentration of N
atoms detected by the vuv-LIF method was obtained. The
inner NO injection tube is movable so that the reaction time
can be varied by changing the location of the addition of theNO molecules. To check the wall reactivity of N(4S), thetitration experiments were carried out under different
residence time conditions (0.2 – 0.5 s) by changing thelocation of the NO injection. No significant influence fromthe wall loss of N(4S) atoms was observed, which isconsistent with the very low wall reactivity reported by
Wennberg et al. [1994].
[13] Fluorescence excitation spectra for N(4S) atoms
produced in the N2O photolysis at 193 nm and the MW
discharge of N2 were measured to determine the quantum
yield for N(4S) formation in the N2O photolysis. The N(4S)
production quantum yield from the photolysis of N2O, N,
is defined by the number density of N(4S) atoms produced
from the photolysis divided by the number density of N2O

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NAKAYAMA ET AL.: N(4S) PRODUCTION FROM N2O

the vuv-LIF detection and the N atom concentration
calibration.

Figure 3. Plots of the titration for the N atoms producedby the microwave discharge of N2. The horizontal axis is
the NO concentration added downstream of the discharge.
The vertical axis is the LIF intensity of N(4S). The solid line
indicates the results of the first-order least squares fitting.

3.2. Photolytic Calibration Method[14] Cl(2P1/2) atoms produced from HCl photolysis at
193 nm were detected by the vuv-LIF technique at
120.135 nm, which is associated with electronic transitionof Cl(3p44s 2D3/2
3p5 2P1/2). The tunable vuv laser
radiation around 120.135 nm was also obtained with thesame experimental setup for the vuv laser system with theHg vapor cell and the fluorescence detection system.
Figure 4 shows the fluorescence excitation spectrum forCl(2P1/2) atoms produced in the 193 nm photolysis of HCl.
A gas mixture of HCl/Ar (12.3% of HCl in Ar) was used.
By comparing the relative intensities of LIF signals of N(4S)from N2O and Cl(2P1/2) from HCl photolysis, the N(4S)
quantum yield can be estimated. Experimentally, measurements of spectra for N and Cl atom were alternatively
performed by changing both the reactants and laser
wavelengths.
[15] The quantum yield for N(4S) formation, N, from thephotolysis of N2O at 193 nm is obtained by the following
equation:
N ¼

molecules excited by the photolysis laser light at 193 nm,
which is expressed as follows:N ¼ðAPh =AMW Þ½N MW FMW
sN2O ½N2 O IPh
FPh

ð4Þ

APh and AMW are the areas of the resonance peaks of thefluorescence excitation spectra of N(4S) atoms produced in
the photolysis of N2O at 193 nm and in the MW dischargeof N2, respectively, under the same conditions for the N
atom detection. [N]MW is the concentration of N atom
produced in the MW discharge of N2, which calibrated by
the titration technique. sN2O is the photoabsorption crosssection of N2O at 193 nm, 8.95  1020 cm2 molecule1[Sander et al., 2003]. [N2O] is the concentration of N2O inthe chamber. IPh is the photon density of the incident
photolysis laser light, which was measured to be 8.4 1016 photons cm2. Intensity variation of the photolysis
laser light was small (<5%) throughout the measurements.
FPh and FMW are the detection efficiencies of thefluorescence monitoring in the photolysis and MW
discharge experiments, respectively, where the excitation
volume by the probe vuv laser in the chamber, the overlap
region of the 193 nm photolysis laser with the probe laser,
and the solid angle from the emitting region onto thephotocathode of the PMT are take into account. The lengthof the volume excited by the probe laser in the viewing zoneof the PMT was 15 mm, while that of the volume where theprobe laser beam overlapped with the photolysis laser was
6 mm. Therefore the value of F(MW)/F(ph) was estimatedto be 2.5. Three sets of experiments were performed for thechemical titration method. Consequently, N was determined to be 2.25 (±0.71)  103. The quoted error includes
the 1s statistical and estimated systematic uncertainties for

AN ICl sHCl ½HCl f Cl jClCl
ACl IN sN2O ½N2 O f N jN

ð5Þ

AN and ACl are the areas of resonance peaks in the
fluorescence excitation spectra of N(4S) atoms in thephotolysis of N2O and Cl( 2P1/2) atoms in the photolysis ofHCl, respectively. IN and ICl are the relative probe laser
intensities for N and Cl atom detection which obtained as aphotoionization current from the NO containing cell. The
photoionization efficiencies of NO molecule used at120.071 and 120.135 nm are also taken into account [Onoet al., 1980; Erman et al., 1995]. sHCl is the photoabsorption
cross section of HCl at 193 nm, 8.69  1020 cm2
molecule1 [Sander et al., 2003]. [HCl] is the concentrationof HCl molecules in the chamber. fN and fCl are the
2p3 4S3/2)
oscillator strength values for the N(2p23s 4P1/2
45 2
2
3p P1/2) optical excitation. The
and Cl(3p 4s D3/2

Figure 4. Fluorescence excitation spectra of Cl(2P1/2)
atoms produced from the 193 nm photolysis of HCl.

NAKAYAMA ET AL.: N(4S) PRODUCTION FROM N2O

values of fN and fCl are taken from the database of National
Institute of Standards and Technology [2003]. jN and jCl
indicate the detection efficiencies of the resonance fluorescence for N and Cl atoms, respectively. As for Cl(2P1/2)
atom detection, the excited Cl(2D3/2) state fluoresces
at 120.135 and 118.875 nm, which are resonant to the2
D3/2 ! 2P1/2 and 2D3/2 ! 2P3/2 transition, respectively.
The detection efficiencies of the PMT system among the
wavelengths at 120.071, 120.135 and 118.875 nm for theN(4P1/2 ! 4S3/2), Cl(2D3/2 ! 2P1/2) and Cl(2D3/2 ! 2P3/2)
emission lines, respectively, are assumed to be constantsince those wavelength are very close. The quantum yield of
Cl(2P1/2) atoms in the photolysis of HCl at 193 nm
photolysis, Cl, is reported to be 0.408 [Zhang et al.,1997]. In this experiment, the collisional relaxation and thechemical reaction of Cl(2P1/2) could be ignored. The
pressures of HCl and Ar buffer gas were 20 and 160 mTorr
and the time delay between the photolysis and probe laser
pulses was 130 ns, and the relaxation rate of Cl(2P1/2) bycollision with HCl and Ar are 7.8  1012 and 1.0 
1014 cm3 molecule1 s1, respectively [Hitsuda et al.,
2001; Sotnichenko et al., 1988]. Twenty-three sets ofexperiments were performed for photolytic calibration
method. Consequently, N = 1.70 (±1.21)  103 was
obtained. The quoted error includes the 1s statistical andestimated systematic uncertainties.
[16] The results obtained from the two different experiments of the chemical titration and photolytic calibration
methods are in good agreement with each other within theexperimental uncertainties. The quantum yield value for
N(4S) formation in the 193 nm photolysis of N2O isdetermined to be N = 2.1 (±0.9)  103 by combining
the experiments results from two methods, in which the
majority of the error from each of the two methods are
systematic uncertainties.

4. Discussion
4.1. Dissociation Process of N2O to Produce
N(4S) + NO[17] In the photolysis of N2O around 200 nm, there are
four energetically available dissociation pathways (1) – (1000).
In this work, we determined the quantum yield for N(4S)
production in the photolysis of N2O at 193 nm. Our result ofN = 2.1 (±0.9)  103 is smaller than the upper limit value
presented by Greenblatt and Ravishankara [1990]. They
estimated the NO production yield (channel (10)) by
observing the chemiluminescence of NO2 that was formedby the reaction of O3 and NO fragments produced from N2O
photolysis. A quite small quantum yield value can be
explained by a spin-forbidden nature for channel (10).
[18] Figure 5 shows the correlation diagram for thereactions of O + N2 and NO + N, in which Cs symmetry
is assumed for the reaction intermediate [Hopper, 1984].
N2O has 16 valence electrons and belongs to C1v symmetrygroup when it is in its electronic ground state X 1+(4s25s26s21p47s22p4 configuration). The lowest electronically exited singlet states are the A 1, the B 1, and the
C 1 states. Upon bending the Cs symmetry group applies
giving rise to the 1 1A0 (1+) and the 1 1A00 (1) states. The
 and  states split into A0 and A00 components. The
theoretical calculations by Hopper [1984] show that disso-

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Figure 5. Adiabatic correlation diagram for N2O (N-NO,
N2O, and N2-O) system assuming a Cs symmetry, which istaken from Hopper [1984]. The energy levels are drawn toscale.

ciation around 200 nm occurs via the 2 1A0 state, and that the
nearby 1 1A00 state can also be involved in the dissociation
process. While the 2 1A0 state is part of a Renner-Teller pair,the component of this pair has a linear equilibrium geometry
and its energy increases rapidly as the molecule bends. Teuleet al. [2000] studied the photodissociation of N2O around 203
nm by a technique of photofragment imaging, and showedthat the parallel transition to the 2 1A0 state is dominant.
[19] Previous studies showed that channel (1) is dominantwith almost unity quantum yield in the 193 nm photolysis of
N2O [Okabe, 1978], which is rationalized by the fact thatboth the 2 1A0 and 1 1A00 states adiabatically correlate to thephotoproducts of O(1D) + N2 (channel (1)). In the present
study, the N(4S) atom formation (channel (10)) is observed
directly by the vuv-LIF method and the quantum yield isdetermined to be 2.1 (±0.9)  103. The adiabatic correlation diagram shown in Figure 5 suggests that the intersystem crossing from the excited singlet state to the triplet state
or direct photoexcitation to the triplet states can account for
the N(4S) formation. A weak spin-orbit interaction between
the singlet and triplet excited states or a small transition
probability from the ground to the triplet states may resultsin the very small quantum yield for N(4S) formation in N2O
photolysis at 193 nm.
4.2. Atmospheric Implications[20] We have investigated the atmospheric importanceof channel (10). A gap between the Shumann-Runge bandof O2 and the Hartley band of O3 allows far ultraviolet
solar radiation to reach the stratosphere. The wavelength
region around 200 nm is known as ‘‘atmospheric window’’ in the stratosphere. The stratospheric sink of N2O
is mainly due to UV photolysis in the atmosphericwindow region. The remaining sink of N2O is reaction
with O(1D) which is produced by the ozone photolysis.

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Reaction (2a) is an important source of stratospheric NO.
The photolysis of N2O proceeding via photodissociation
channel N(4S) + NO can also provide a stratospheric NO
source.
[21] The current NASA/JPL evaluation [Sander et al.,2003] for stratospheric modeling recommends that thequantum yield for photodissociation of N 2 O around200 nm is unity, and the products are N2 and O(1D)(channel (1)). However, the N(4S) and NO(2) formation(channel (10)) can be a nonnegligible direct source ofstratospheric NOx (= N + NO + NO2). The stratospheric
O3 abundance and its vertical profile are significantly
affected by NOx, because NOx can catalytically destroy
stratospheric O3. In this study, we have investigated theatmospheric importance of channel (10) in the photolysis of
N2O, by using a one-dimensional dynamical-photochemical
model. All chemical schemes of the model are the samewith that in the Garcia-Solomon two-dimensional (GS-2D)
model [Solomon et al., 1996]. The model calculations were
performed including 40 chemical species and 120 chemical
reactions with the chemical kinetics and photochemical
data presented by the recent JPL recommendations [Sander
et al., 2003]. We included channel (10) quantum yield valueof 2.1  103 in the model on the assumption that it isindependent of the temperature and wavelength at theatmospheric window region.
[22] Figure 6 shows the result of the photochemical
model calculations for latitude of 40 in March, whichindicates the change in the diurnally averaged concentrations of NOx, HOx (= H + OH + HO2), ClOx (= Cl + ClO)
and O3 calculated with or without channel (10) in thephotolysis of N2O. The steady state NOx concentration
calculated by the model including channel (10) increases
up to 3% around 25 km in comparison with that ignoring
channel (10), while the HOx and ClOx abundances decrease.
The altitude-dependent change in the NOx concentration
should reflect the altitude-dependent solar flux at theatmospheric window wavelength region. The perturbationsin the concentrations of HOx and ClOx may be attributable
to the following reactions:OH þ NO2 þ M ! HNO3 þ M

ð6ÞClO þ NO2 þ M ! ClONO2 þ M

ð7ÞOH þ HCl ! Cl þ H2 O:

ð8ÞThe concentration changes of HOx and ClOx are larger inthe lower stratosphere as shown in Figure 6, because thecontribution of three-body reactions (6) and (7) becomes
more significant at lower stratospheric altitudes.
Reaction (8) converts the chlorine reservoir HCl into
active ClOx. The decrease of the HOx concentration may
result in the decrease of ClOx through reaction (8). The
chemical reactions of NOx, HOx and ClOx families play a
crucial role in determining the stratospheric O3 abundance, and thus the concentration changes of these
species alter O3 abundance. Inclusion of channel (10) in
the model affects the production rate of NOx, which isfollowed by the decrease of O3 abundance through the

Figure 6. Calculated percentage changes in NOx, HOx,
ClOx, and O3 concentrations with the N(4S) + NO
dissociation channel from those calculated without theN(4S) + NO channel for latitude of 40 in March as afunction of altitude.
enhancement of the NOx catalyzed O3 destruction rate, as
shown in Figure 6.
[23] The chemical reactions involving the nitrogen atoms
play a crucial role in the Earth’s and planetaries’ atmospheres [Yung and DeMore, 1999]. For example, the reaction of N(4S) with O2 can be an important NO source in the
Earth’s lower thermosphere, where the N(4S) atoms areproduced by the solar vacuum and extreme ultraviolet
photolysis of NO molecules [Dothe et al., 1997]. In the
Titan’s atmosphere, the reactions of N(4S) atoms withhydrocarbons are important as a source of highly reactive
CN radicals. Therefore it is essential for understanding theterrestrial atmospheric processes to study the chemical
reactions of nitrogen atoms. In this study, the ground statenitrogen atom, N(4S), was detected directly by the laserinduced fluorescence technique at 120.071 nm. N(4S) atom
was produced in the photolysis of N2O at 193 nm or
microwave discharge of N2. This is the first report of the
vuv-LIF detection of N(4S) atom as far as we have searched.
The minimum detection limit is estimated to be 2 
109 atoms cm3 under our experimental conditions. The
pulsed photodissociation of N2O molecules and high-sensitivity detection technique for N(4S) atom are applicable tothe studies of the kinetics and dynamics of the chemical
reaction processes involving N(4S) atoms.
[24] Acknowledgments. This work was partly supported by grant-inaid from the Ministry of Education, Culture, Sports, Science and Technology, Japan. This work is also partly supported by Steel Industrial Foundation
for the Advancement of Environmental Protection Technology. The authors
thank Koichi Tsukiyama (Tokyo University of Science) for his advice in thetechniques of vuv generation. N. T. thanks the Japan Society for Promotionof Science for a fellowship for young scientists. The one-dimensional model
used in this study was originally offered by Susan Solomon, NOAA
Aeronomy Laboratory.

NAKAYAMA ET AL.: N(4S) PRODUCTION FROM N2O

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Y. Matsumi, T. Nakayama, and K. Takahashi, Solar-Terrestrial Environment Laboratory and Graduate School of Science, Nagoya University,
Honohara 3-13, Toyokawa, Aichi, 442-8507, Japan. (matsumi@stelab.
nagoya-u.ac.jp; nakayama@stelab.nagoya-u.ac.jp; kent@stelab.nagoya-u.
ac.jp)
S. Hayashida and N. Taniguchi, Faculty of Science, Nara Women’s
University, Kitauoya-Nishimachi, Nara, 630-8506, Japan. (sachiko@ics.
nara-wu.ac.jp; ntanig@ics.nara-wu.ac.jp)