Photodissociation dynamics of the methyl radical at 212.5 nm: Effect of parent internal excitation.

Photodissociation dynamics of the CH[sub 3] radical at 212.5 nm has been investigated using the H atom Rydberg tagging time-of-flight method with a pure CH[sub 3] radical source generated by the photolysis of CH[sub 3]I at 266 nm. Time-of-flight spectra of the H atom products from the photolysis of both cold and hot methyl radicals have been measured at different photolysis polarizations. Experimental results indicate that the photodissociation of the methyl radical in its ground vibrational state at 212.5 nm excitation occurs on a very fast time scale in comparison with its rotational period, indicating the CH[sub 3] dissociation at 212.5 nm occurs on the excited 3s Rydberg state surface. Experimental evidence also shows that the photodissociation of the methyl radical in the ν[sub 2]=1 state of the umbrella mode at 212.5 nm excitation is characteristically different from that in the ground vibrational state. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]