Overtone-induced dissociation and isomerization dynamics of the hydroxymethyl radical (CH 2 OH and CD 2 OH). II. Velocity map imaging studies

The dissociation of the hydroxymethyl radical, CH 2 OH, and its isotopolog, CD 2 OH, following excitation in the 4ν 1 region (OH stretch overtone, near 13 600 cm −1 ) was studied using sliced velocity map imaging. A new vibrational band near 13 660 cm −1 arising from interaction with the antisymmetric CH stretch was discovered for CH 2 OH. In CD 2 OH dissociation, D atom products (correlated with CHDO) were detected, providing the first experimental evidence of isomerization in the CH 2 OH ↔ CH 3 O (CD 2 OH ↔ CHD 2 O) system. Analysis of the H (D) fragment kinetic energy distributions shows that the rovibrational state distributions in the formaldehyde cofragments are different for the OH bond fission and isomerization pathways. Isomerization is responsible for 10%-30% of dissociation events in all studied cases, and its contribution depends on the excited vibrational level of the radical. Accurate dissociation energies were determined: D 0 (CH 2 OH → CH 2 O + H) = 10160 ± 70 cm −1 , D 0 (CD 2 OH → CD 2 O + H) = 10135 ± 70 cm −1 , D 0 (CD 2 OH → CHDO + D) = 10760 ± 60 cm −1 .