²A¢ (3p)¬ ²A² spectra of the isotopically substituted hydroxymethyl radicals (CH₂OH, CH₂OD, CD₂OH, CD₂OD) were observed between 39700 and 43000 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 n ₈ torsion modes and n ₉ CH₂-wag mode are strongly coupled and governed by nonharmonic potential energy functions, e.g., for ¹²CH₂¹⁶OH( ²A² ) we obtain 2n ₈= 846 ± 6 cm^-1, 1n ₉= 234 ± 5 (1s ) cm^-1, and 2n ₉= 615 ± 6 cm^-1. Using MP2/6-311G(2df,2p) ab initio calculations, we constructed the two-dimensional potential energy surfaces that govern the n ₈ torsion modes and n ₉ CH₂-wag in ²A² radical and the ¹A¢ cation core of the ²A¢ (3p) Rydberg state. Energy levels calculated with these potential energy surfaces account for the REMPI bands originating from the n ₈ hindered rotor and the n ₉ CH₂-wag modes. The experimental and ab initio results lead to improved heat capacities and entropies ((CH₂OH) = 244.2 J-(mole-K)-1). Ab initio CBS-QCI/APNO calculations predict that(CH₂OH) = -18.4 ± 1.3 kJ-mole-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 (CH₂OH⁺) = 717.6 ± 0.5 kJ-mole-1, (CH₂OH⁺) = 715.9 ± 0.5 kJ-mole-1, (CH₂OH) = -12.0 ± 0.4 kJ-mole-1, and (CH₂OH) = -18.3 ± 0.4 kJ-mole-1. Thermochemical tables based upon these values are presented for CH₂OH and CH₂OH⁺.