Distributions of angular anisotropy and kinetic energy of products from the photodissociation of methanol at 157 nm

We investigated distributions of angular-anisotropy parameter β and kinetic energy of fragments after photodissociation of methanol using time-of-flight (TOF) mass spectrometry. Fragments, in particular CH3O and CO, were successfully detected using tunable radiation from a synchrotron for photoionization. Following O-H bond fission, a CH3O fragment with internal energy greater than 104 kJ mol-1 dissociates to CH2O+H. Elimination of two H2 accompanies formation of CO. The <β> value of hydroxyl hydrogen is -0.26 whereas that of methyl hydrogen is zero. H2 has two distinct components in TOF spectra; these rapid and slow components have <β> values -0.30 and -0.18, respectively. The CH3+OH dissociation exhibits a highly anisotropic angular distribution with <β>=-0.75. The β values of fragments from CD3OH photolysis are addressed. From measurements of angular-anisotropy parameters of various fragments, we surmise that the transition dipole moment μ is almost perpendicular to the C-O-H plane and that n-3px (2 1A'') is the major photoexcited state at 157 nm