(B) over tilde(2)A’(3p) <-- (X) over tilde(2)A " spectra of the isotopically 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. Analyses of the vibrational hot bands in these spectra show that the nu(8) torsion 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). Using MP2/6-311G(2df,2p) nb initio calculations, we constructed the two-dimensional potential energy surfaces that govern the nu(8) torsion modes 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 state. Energy levels calculated with these potential energy surfaces account 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 equilibrium data, and shock tube data indicate that Delta(f)H degrees(0)(CH2OH+) = 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+.