DIRECT KINETIC-STUDIES OF THE REACTIONS BR- THE HEAT OF FORMATION OF CH2OH(CH3OH AND CH2OH+HBR )

The chemical equilibrium Br + CH3OH reversible arrow HBr + CH2OH (1, - 1) has been studied by investigating the kinetics of the forward and r everse reactions. Excimer laser photolysis coupled with Br atom resona nce fluorescence detection was used over the temperature range 439-713 K to obtain k(1) = (3.41 +/- 0.89) x 10(9)T(1.5) exp[-(29.93 +/- 1.47 ) kJ mol(-1)/RT] cm(3) mol(-1) s(-1). The reverse reaction was studied with the fast flow technique, in the temperature range 220-473 K, usi ng laser magnetic resonance for monitoring the CH2OH radicals. Thus, k (-1) = (1.20 +/- 0.25) x 10(12) exp[(3.24 +/- 0.44) kJ mol(-1)/RT] was obtained. The kinetic results were compared with available literature data and possible causes of the deviations were discussed. Kinetic in formation on the foward and back reactions was combined to obtain the heat of formation for CH2OH. Both second-law and third-law procedures were used in the derivations, giving a recommended value of Delta(f)H degrees(298)(CH2OH) = -16.6 +/- 1.3 kJ mol(-1), which corresponds to t he C-H bond dissociation energy of DH degrees(298)(H-CH2OH) = 402.3 +/ - 1.3 kJ mol(-1). These thermochemical data obtained from kinetic equi librium studies agree within the error limits with current photoioniza tion mass spectrometric and ab initio theoretical results.