STRUCTURAL AND THERMOCHEMICAL PROPERTIES OF HYDROXYMETHYL (CH2OH) RADICALS AND CATIONS DERIVED FROM OBSERVATIONS OF (B)OVER-TILDE (2)A'(3P)[-(X)OVER-TILDE (2)A'' ELECTRONIC-SPECTRA AND FROM AB-INITIO CALCULATIONS
Rd. Johnson et Jw. Hudgens, STRUCTURAL AND THERMOCHEMICAL PROPERTIES OF HYDROXYMETHYL (CH2OH) RADICALS AND CATIONS DERIVED FROM OBSERVATIONS OF (B)OVER-TILDE (2)A'(3P)[-(X)OVER-TILDE (2)A'' ELECTRONIC-SPECTRA AND FROM AB-INITIO CALCULATIONS, Journal of physical chemistry, 100(51), 1996, pp. 19874-19890
(B) over tilde(2)A'(3p) <-- (X) over tilde(2)A '' spectra of the isoto
pically substituted hydroxymethyl radicals (CH2OH, CH2OD, CD2OH, CD2OD
) were observed between 39 700 and 43 000 cm(-1) by 2+1, 2+2, and 1+1
resonance-enhanced multiphoton ionization (REMPI) spectroscopy. Analys
es of the vibrational hot bands in these spectra show that the nu(8) t
orsion modes and nu(9) CH2-wag mode are strongly coupled and governed
by nonharmonic potential energy functions; for example, for (CH2OH)-C-
12-O-16((X) over tilde(2)A '') we obtain 2 nu(8) = 846 +/- 6 cm(-1)(1
sigma), 1 nu(9) = 234 +/- 5 cm(-1), and 2 nu(9) = 615 +/- 6 cm(-1). Us
ing MP2/6-311G(2df,2p) nb initio calculations, we constructed the two-
dimensional potential energy surfaces that govern the nu(8) torsion mo
des and nu(9) CH2-wag in the (X) over tilde(2)A '' radical and the (X)
over tilde(1)A' cation core of the (B) over tilde(2)A'(3p) Rydberg st
ate. Energy levels calculated with these potential energy surfaces acc
ount for the REMPI bands originating from the nu(8) hindered rotor and
the nu(9) CH2-wag modes. The experimental and nb initio results lead
to improved heat capacities and entropies (S degrees(298.15)(CH2OH) =
244.170 +/- 0.018 J (mol K)(-1)). Ab initio CBS-QCI/APNO calculations
predict that Delta(f)H degrees(298.15)(CH2OH) = -18.4 +/- 1.3 kJ mol(-
1). Re-evaluation of photoionization data yields IPa(CH2OH) = 7.562 +/
- 0.004 eV. Re-evaluated photoionization appearance data, kinetic equi
librium data, and shock tube data indicate that Delta(f)H degrees(0)(C
H2OH+) = 718.1 +/- 1.8 kJ mol(-1), Delta(f)H degrees(298.15)(CH2OH+) =
716.4 +/- 1.8 kJ mol(-1), Delta(f)H degrees(0)(CH2OH) = -11.5 +/- 1.3
kJ mol(-1), and Delta(f)H degrees(298.15)(CH2OH+) = -17.8 +/- 1.3 kJ
mol(-1), We report the proton affinity, PA(0)(CH2O) = 705.2 +/- 1.9 kJ
mol(-1). Thermochemical tables based upon these values are presented
for CH2OH and CH2OH+.