+--------------------------------+----+--------------------------------+
| **x.x.x. Oxomethyl (formyl)    |    | #### 2597-44-6                 |
| radical**                      |    |                                |
+--------------------------------+----+--------------------------------+
| **HC=O (^2^A\')**              |    | **C~S~** (~ext~ = 1)           |
+--------------------------------+----+--------------------------------+
|                                |    |                                |
+--------------------------------+----+--------------------------------+
| ~f~*H*(298.15 K) = 42.3 ± 1.0  |    | ~f~*H*(0 K) = 41.9 ± 1.0 kJ    |
| kJ mol^-1^                     |    | mol^-1^                        |
+--------------------------------+----+--------------------------------+
| *C~p~*(298.15 K) = 34.590 J    |    | *H*(298.15 K) -- *H*(0 K) =    |
| K^-1^ mol^-1^                  |    | 10.001 kJ mol^-1^              |
+--------------------------------+----+--------------------------------+
| *S*(298.15 K) = 224.355 J      |    | *p* = 100 000 Pa (1 bar)       |
| K^-1^ mol^-1^                  |    |                                |
+--------------------------------+----+--------------------------------+

+--------------+----------------------------+--------------+----------+
| **Literature |                            |              |          |
| Data for the |                            |              |          |
| Enthalpy of  |                            |              |          |
| Formation at |                            |              |          |
| 298.15 K**   |                            |              |          |
+--------------+----------------------------+--------------+----------+
| **~f~*H*/kJ  | #### Authors and Reference | ####         | **Co     |
| mol^-1^**    |                            | # Method ^a^ | mments** |
+--------------+----------------------------+--------------+----------+
| *M           |                            |              |          |
| easurements* |                            |              |          |
+--------------+----------------------------+--------------+----------+
| 41.8 ± 0.8   | Chuang *et al.* (1987)[^1] | KPD          | (1a)     |
+--------------+----------------------------+--------------+----------+
| 42.5 ± 0.5   | Terentis and Kable         | KEPD         | (1b)     |
|              | (1996)[^2]                 |              |          |
+--------------+----------------------------+--------------+----------+
| 44.29 ± 0.43 | Bercera *et al.*           | KFP          | (1c)     |
|              | (1997)[^3]                 |              |          |
+--------------+----------------------------+--------------+----------+
| *C           |                            |              |          |
| omputations* |                            |              |          |
+--------------+----------------------------+--------------+----------+
| 38.9 ± 7.1   | Zachariah *et al.*         | BAC-MP4      | (1d)     |
|              | (1996)[^4]                 |              |          |
+--------------+----------------------------+--------------+----------+
| 37.81        | Janoschek (2001)[^5]       | G3MP2B3      | (1e)     |
+--------------+----------------------------+--------------+----------+
| 42\.         | Martin (2001)[^6]          | W2           | (1f)     |
+--------------+----------------------------+--------------+----------+
| 42.3 ± 0.8   | Marenich and Boggs         | AI           | (1g)     |
|              | (2003)[^7]                 |              |          |
+--------------+----------------------------+--------------+----------+
| *Reviews and |                            |              |          |
| Evaluations* |                            |              |          |
+--------------+----------------------------+--------------+----------+
| 43.51 ± 8.   | Chase (1970)[^8]           | CDE-TN       | (1h)     |
+--------------+----------------------------+--------------+----------+
| 37.24 ± 5.   | McMillen and Golden        | CDE          | (1i)     |
|              | (1982)[^9]                 |              |          |
+--------------+----------------------------+--------------+----------+
| 42\. ± 5.    | Gurvich *et al.*           | CDE          | (1j)     |
|              | (1991)[^10]                |              |          |
+--------------+----------------------------+--------------+----------+
| 41.7 ± 0.8   | Berkowitz *et al.*         | CDE          | (1k)     |
|              | (1994)[^11]                |              |          |
+--------------+----------------------------+--------------+----------+
| 42 ± 4       | Tsang (1996)[^12]          | TT-A         | (1l)     |
+--------------+----------------------------+--------------+----------+
| 41.8 ± 4.2   | JPL (1997)[^13]            | TT-A         | (1m)     |
+--------------+----------------------------+--------------+----------+
| 41.3         | Atkinson *et al.*          | TT-A         | (1n)     |
|              | (2000)[^14]                |              |          |
+--------------+----------------------------+--------------+----------+
| 42\. ± 0.8   | Burcat (2001)[^15]         | TT-A         | (1o)     |
+--------------+----------------------------+--------------+----------+
| 43.1         | Kerr (2002)[^16]           | TT-U         | (1p)     |
+--------------+----------------------------+--------------+----------+
| 43.51        | NIST WebBook(2005)[^17]    | TT-A         | (1q)     |
+--------------+----------------------------+--------------+----------+

^a^ KFP: Kinetic flash photolysis reactions; KPD: Kinetic
photodissociation; KEPD : Kinetics of Exciting and Population
Distribution Change; CDE: Critical data evaluation; TT-A: Annotated
tabulation of thermodynamic data; TT-U: Unannotated tabulation of
thermodynamic data.

^b^ The quoted value was either not given explicitly by the author(s) or
it was recalculated using auxiliary thermochemical values that differ
from those used by the original authors; see individual comments for
additional details.

^c^ The uncertainty was either not given explicitly by the original
author(s) or it has been modified; see individual comments for further
explanations.

Comments on the Enthalpies of Formation

 

(1a) The enthalpy of formation of the formyl radical.was obtained from
the measurement of the threshold for the onset of photodissociation of
CH~2~O.

(1b) The CHO radical was produced from the photolysis of H~2~CO very
near to the energy threshold. Rovibronically resolved excitation of the
formaldehyde molecule is followed by high resolution laser-induced
fluorescence excitation spectroscopy of the nascent HCO fragment.

(1c) CHO was generated by flash photolysis of acetaldehyde in order to
obtain rate constants for its bimolecular reactions with HI and HBr.
Combination with known kinetic data on the reverse reaction leads to the
thermodynamic estimate of *~f~H*~298~ = 44.29 kJ mol^-1^ by the third
law method. By the second law method the value obtained is 42.76 ± 0.85
-- 45.27 ± 0.81 kJ mol^-1^.

(1d) *Ab initio* G2 BAC-MP4 calculations for the C/H/O/F system of
molecules and radicals. *~f~H*~0~ = 38.91 kJ mol^-1^, the same value as
for 298 K.

(1e) G3(MP2)//B3LYP *ab initio* calculation. The uncertainty quoted in
the table corresponds to twice the average absolute deviation for the
G2/97 test set of 0.99 kcal mol^-1^, which corresponds roughly to 2 or
\~95% confidence limits. The *~f~H*~0~ = 37.45 kJ mol^-1^.

(1f) The value is the W2 calculation. The W1 value is 40.9 kJ mol^-1^.

(1g) *Ab initio* coupled cluster CCSD(T) calculations of equilibrium
geometries, anharmonic force fields, and thermodynamic properties of HCO
and CHO radicals. The research was performed to elucidate the data for
the present report.

(1h) The values of Chase from 1970 are reprinted in the 1998 edition of
JANAF, and these are quoted by NIST.

(1i) The value is based on old kinetic estimates of Benson.[^18]

(1j) Critical evaluation of all data before 1989. This value is based on
two papers of J.G. Calvert J.Chem Phys **29**, 954 (1958) and J. Am.
Chem. Soc. **30**, 1313 (1958) with J.T. Gruver.

(1k) Based on the bond energy given by Chuang *et* *al.Error: Reference
source not found* *D*(H-CHO) = *~f~H*~298~(HCO)=9.99 kcal mol^­-1^ and
the enthalpy of formation of formaldehyde given by GurvichError:
Reference source not found *~f~H*~298~(CH~2~O)=­25.98 kcal mol^­-1^.

(1l) Tsang accepts the value of Gurvich.Error: Reference source not
found

(1m) Round off in kcal mol^-1^ of Gurvich'sError: Reference source not
found/TsangError: Reference source not found value.

(1n) Attkinson quotes the values of BeceraError: Reference source not
found and Chuang.^Error:\ Reference\ source\ not\ found^

(1o) Thermochemical database for combustion quotes JacoxError: Reference
source not found for vibrations and GurvichError: Reference source not
found for the enthalpy of formation.

(1p) No details given.

(1q) The data of JANAFError: Reference source not found and TsangError:
Reference source not found are quoted.

### Preferred Value of the Enthalpy of Formation

∆~f~*H*°(298.15 K) = 42.3 ± 1. kJ mol^-1^

∆~f~*H*°(0 K) = 41.9 ± 1. kJ mol^-1^

The computational research of Marenich and BoggsError: Reference source
not found was undertaken in order to evaluate among the experimental
estimated and calculated values quoted here. Their value is within the
error limits of the experimental values of Terentis and KableError:
Reference source not found and Chuang.Error: Reference source not found
This decision is backed up by the former estimates of Gurvich,Error:
Reference source not found BerkowitzError: Reference source not found
and by the recent calculation of Martin.Error: Reference source not
found

  -------------------- --------- ------ ----------------- ------ ---------- --- -- ------------------ ------------- -- --------- ----------- ----------------- ---------- ------------
  **Geometry (distance                                                                                                                                                    
  in Å, angles in                                                                                                                                                         
  degrees)^(2a)\ ^**                                                                                                                                                      

  Z-Matrix                                                                                            Cartesian                                                           
                                                                                                      Coordinates                                                         

                                                                                                      x                          y                             z          

  C                                                                         C                         0.062574                   0.589085                      0.000000   

  O                    1 1.1827                                             O                         0.062574                   -0.593577                     0.000000   

  H                    1 1.1277                                             H                         -0.876042                  1.214106                      0.000000   
                       2 123.660                                                                                                                                          

                                                                                                                                                                          

  **Moments of Inertia                                                                                                                                                    
  in the Electronic                                                                                                                                                       
  Ground State^(2b)^**                                                                                                                                                    

  *I*~A~ = 1.13968                                               *I*~B~ =                                              *I*~C~ =                                           
  10^-47^ kg m^2^                                                18.68676                                              19.9521                                            
                                                                 10^-47^ kg                                            10^-47^                                            
                                                                 m^2^                                                  kg m^2^                                            

                                                                                                                                                                          

  **[Bond Distances                                                                                                                                                       
  (10^-10^ m)                                                                                                                                                             
  ^(2b)^]{.mark}**                                                                                                                                                        

  [*r*(C H): 1.117                                                                                                                                                        
  *r*(C -- O): 1.174                                                                                                                                                      
  *a*(HCO):                                                                                                                                                               
  124.6]{.mark} (i                                                                                                                                                        
  don't like removing                                                                                                                                                     
  info, but we don't                                                                                                                                                      
  usually include                                                                                                                                                         
  these)                                                                                                                                                                  

                                                                                                                                                                          

  **Vibrational                                                                                                                                                           
  Wavenumbers in the                                                                                                                                                      
  Electronic Ground                                                                                                                                                       
  State (*~i~* /                                                                                                                                                          
  cm^-1^) ^(2c)^**                                                                                                                                                        

  1097                           1885                     2465                                                                                                            

                                                                                                                                                                          

  **Ground State                                                                                                                                                          
  Anharmonicity                                                                                                                                                           
  Constants^(2c)^**                                                                                                                                                       

  *x*~11~ = −12.703                     *x*~12~ = −1.741                           *x*~13~ = −4.409                                          *x*~22~ = −10.346            

  *x*~23~ = −6.610                      *x*~33~ =                                  α~1~^A^=2.041                                             α~2~^A^=−0.0938              
                                        −124.441                                                                                                                          

  α~3~^A^= −1.509                       α~1~^B^=0.00530                            α~2~^B^=−0.0119                                           α~3~^B^= 0.000372            

  α~1~^C^= −0.00544                     α~2~^C^=−0.0110                            α~3~^C^=−0.00349                                                                       
  -------------------- --------- ------ ----------------- ------ ---------- --- -- ------------------ ------------- -- --------- ----------- ----------------- ---------- ------------

.

**Heat Capacity *C*°*~p~*, Entropy *S*° and Enthalpy Increment
\[*H*°(*T*) -*H*°(0 K)\] ^(2d)^**

+----------------+-----------------+---------------+------------------+
| ***T*/K**      | > ***           | >             | > **\[*H*°(*T*)  |
|                | C*°*~p~*(*T*)** | ***S*°(*T*)** | > -*H*°(0 K)\]** |
|                | >               |               | >                |
|                | > (J K^-1^      | (J K^-1^      | > (kJ mol^-1^)   |
|                | > mol^-1^)      | mol^-1^)      |                  |
+----------------+-----------------+---------------+------------------+
| 150            | 33.35           | 201.09        | 4.988            |
+----------------+-----------------+---------------+------------------+
| 200            | 33.54           | 210.70        | 6.659            |
+----------------+-----------------+---------------+------------------+
| 250            | 34.00           | 218.23        | 8.347            |
+----------------+-----------------+---------------+------------------+
| 298.15         | 34.68           | 224.28        | 10.000           |
+----------------+-----------------+---------------+------------------+
| 300            | 34.71           | 224.49        | 10.064           |
+----------------+-----------------+---------------+------------------+
| 350            | 35.60           | 229.91        | 11.821           |
+----------------+-----------------+---------------+------------------+
| 400            | 36.61           | 234.72        | 13.626           |
+----------------+-----------------+---------------+------------------+
| 500            | 38.85           | 243.13        | 17.397           |
+----------------+-----------------+---------------+------------------+
| 600            | 41.2            | 250.40        | 21.398           |
+----------------+-----------------+---------------+------------------+
| 700            | 43.4            | 256.9         | 25.626           |
+----------------+-----------------+---------------+------------------+
| 800            | 45.4            | 262.9         | 30.066           |
+----------------+-----------------+---------------+------------------+
| 900            | 47.2            | 268.3         | 34.699           |
+----------------+-----------------+---------------+------------------+
| 1000           | 48.8            | 273.4         | 39.504           |
+----------------+-----------------+---------------+------------------+
| 1500           | 54.5            | 294.4         | 65.473           |
+----------------+-----------------+---------------+------------------+
| 2000           | 58.1            | 310.6         | 93.667           |
+----------------+-----------------+---------------+------------------+
| 2500           | 61.1            | 323.8         | 123.468          |
+----------------+-----------------+---------------+------------------+
| 3000           | 63.8            | 335.2         | 154.687          |
+----------------+-----------------+---------------+------------------+

^\*^ The pressure at which this table was calculated is *p* = 101325 Pa.

**7-Constant NASA Polynomial**

CHO Formyl Rad IU5/03C 1.H 1.O 1. 0.G 200.000 6000.000 29.01804 1

3.92001542E+00 2.52279324E-03-6.71004164E-07
1.05615948E-10-7.43798261E-15 2

3.65342928E+03 3.58077056E+00 4.23754610E+00-3.32075257E-03
1.40030264E-05 3

-1.34239995E-08 4.37416208E-12 3.87241185E+03 3.30834869E+00
5.08749163E+03 4

**9-Constant NASA Polynomial**

CHO Formyl Radical IUPAC Task Group for Selected Radicals

3 IU5/03 C 1.00H 1.00O 1.00 0.00 0.00 0 29.0180400 42300.000

50.000 200.000 7 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 0.0 10000.000

1.909054361D+02-6.505083940D+00 4.007960170D+00
1.976299520D-03-2.595595158D-05

1.244398772D-07-1.867688014D-10 0.000000000D+00 3.911446940D+03
3.943182620D+00

200.000 1000.000 7 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 0.0 10000.000

-9.217964230D+02 2.491028603D+01 4.021945390D+00-2.474162328D-03
1.235893571D-05

-1.190013708D-08 3.838988660D-12 0.000000000D+00 3.765811090D+03
4.423377420D+00

1000.000 6000.000 7 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 0.0 10000.000

2.077147739D+06-8.433987270D+03 1.602453231D+01-5.394244960D-03
1.859525520D-06

-2.779868187D-10 1.457229515D-14 0.000000000D+00
5.509247840D+04-8.065557680D+01

##### Comments on Molecular Data, Heat Capacity, Entropy and Enthalpy Increment

(2a) The geometry coordinates were calculated by Janoschek.Error:
Reference source not found

(2b) The moments of inertia are equivalent to *A*~0~=24.562 cm^-1^,
*B*~0~=1.498 cm^-1^, and *C*~0~=1.403 cm^-1^, and the bond distances
were calculated by Marenich and Boggs.Error: Reference source not found

(2c) The *ab initio* CCSD(T)/vqz calculated wavenumbers and
anharmonicity constants are of Marenich and Boggs.Error: Reference
source not found The experimental vibrational wavenumbers reported by
JacoxError: Reference source not found are T~e~ =0(2), *ω*~e~ = 2435
cm^-1^, 1868 cm^-1^, and 1087 cm^-1^. Serrano-Andres *et* *al.*[^19]
calculated with the CAPT2 optimized geometry method for ground state
wavenumbers 2713, 1877, 1107 cm^-1^ and --134, −13, −15, 3, −7, −5 for
the *x*~11~ *x*~22~ *x*~33~ *x*~12~ *x*~13~ *x*~23~ respectively. The
newer ones, *ab initio* G3MP2B3 wavenumbers, were calculated (unscaled)
by Janoschek:Error: Reference source not found 668 cm^-1^, 1948 cm^-1^,
and 1130 cm^-1^.

(2d) The NASA polynomials were calculated with McBride and Gordon's
PAC99 program.[^20] The values were taken from the tables of Marenich
and BoggsError: Reference source not found since they used direct
summation methods. The standard heat capacity and entropy values
reported in the \"Thermochemical Database for Combustion\"Error:
Reference source not found are *C~p,298~* = 32.459 J mol^-1^ K^-1^,
*S~298~* = 195.638 J mol^-1^ K^-1^.

[^1]: M. C. Chuang, M. F. Foltzand, and C. B. Moore, *J. Chem. Phys*.
    **87**, 3855 (1987).

[^2]: A. C. Terentis and S. H. Kable*, Chem. Phys. Lett.* **258,** 626
    (1996).

[^3]: R. Becerra, I. W. Carpenter, and R. Walsh*, J. Phys. Chem. A*
    **101**, 4185 (1997).

[^4]: M. R. Zachariah, P. R. Westmoreland, .R. Burges Jr., W. Tsang, and
    C. F. Melius, *J. Phys. Chem.* **100**, 8737 (1996).

[^5]: R. Janoschek, calculations for this database,*.*Oct. 2001.

[^6]: S. Parthiban and J. M. L. Martin, *J. Chem. Phys*. **114**, 6014
    (2001).

[^7]: A. V. Marenich and J .E. Boggs, *J. Phys. Chem* **107** 2343
    (2003).

[^8]: M. W. Chase Jr. NIST-JANAF Thermochemical Tables, Fourth Edition*,
    J. Phys. Chem. Ref*. *Data,* Monograph 9. 1998.

[^9]: D. F. McMillen and D. M. Golden, *Ann. Rev. Phys. Chem*. **33**,
    493 (1982).

[^10]: L. V. Gurvich, I. V. Veyts, and C. B. Alcock, *Thermodynamic
    Properties of Individual Substances*, 4^th^ Edition, Vol. 1 & 2,
    Hemisphere, New York, 1989.

[^11]: J. Berkowitz, G. B. Ellison, and D. Gutman, *J. Phys. Chem*.
    **98**, 2744 (1994).

[^12]: [W.
    Tsang.](http://webbook.nist.gov/cgi/cbook.cgi?Author=Tsang,+W.&Units=SI&Mask=1),
    *Heats of Formation of Organic Free Radicals by Kinetic Methods* in
    [Energetics of Organic Free Radicals]{.underline}, Martinho Simoes,
    J.A.; Greenberg, A.; Liebman, J.F., eds., Blackie Academic and
    Professional, London, p.22-58 (1996).

[^13]: W. B. DeMore, S. P. Sander, D. M. Golden, R. F. Hampson, M. J.
    Kurylo, C. J. Howard, A. R. Ravishankara, C. E. Kolb, and M. J.
    Molina, *Chemical Kinetics and Photochemical Data for Use in
    Stratospheric Modeling, Evaluation No. 12*, JPL Publication 97-4,
    NASA and JPL (January 15, 1997).

[^14]: R. Atkinson, D. L. Baulch, R. A. Cox, R. F. Hampson, Jr., J. A.
    Kerr, M. J. Rossi, and J. Troe, *J. Phys. Chem. Ref. Data* **29**,
    167 (2000).

[^15]: A. Burcat, *Third Millennium Ideal Gas and Condensed Phase
    Thermochemical Database for Combustion*, TAE Report No.867,
    Technion, Haifa, 2001. (see also
    [ftp://ftp.technion.ac.il./pub/supported/aetdd/thermodynamics](ftp://ftp.technion.ac.il./pub/supported/eatdd/thermodynamics)).

[^16]: J. A. Kerr, *CRC Handbook of Chemistry and Physics*, 83^rd^
    Edition, 2002. CRC Press, Boca Raton.

[^17]: W. G. Mallard and P. J. Linstrom, Eds**.,** *NIST Chemistry
    WebBook*, NIST Standard Reference Database Number 69**,** February
    2000, National Institute of Standards and Technology, Gaithersburg
    MD, 20899 (<http://webbook.nist.gov/chemistry/>).

[^18]: \(a\) D. M. Golden and S. W. Benson, *Chem. Rev*. **69,** 125
    (1969); (b) S. W. Benson and H. E. O'Neal, in *Free Radicals*,
    Wiley, N.Y. 2:273, (1973).

[^19]: L. Serrano-Andres, N. Fosberg, and P. A. Malmqvist, *J. Chem.
    Phys*. **108**, 7202 (1998).

[^20]: B. McBride and S. Gordon: "Computer Program for Calculating and
    Fitting Thermodynamic functions" Report NASA-RP-1271 (1992).