Productions of I, I*, and C2H5 in the A-band photodissociation of ethyl iodide in the wavelength range from 245 to 283 nm by using ion-imaging detection

Photodissociation dynamics of ethyl iodide in the A band has been investigated at several wavelengths between 245 and 283 nm using resonance-enhanced multiphoton ionization technique combined with velocity map ion-imaging detection. The ion images of I, I-*, and C2H5 fragments are analyzed to yield corresponding speed and angular distributions. Two photodissociation channels are found: I(5p P-2(3/2))+C2H5 (hotter internal states) and I-*(5p P-2(1/2))+C2H5 (colder). In addition, a competitive ionization dissociation channel, C2H5I++h nu -> C2H5+I+, appears at the wavelengths < 266 nm. The I/I-* branching of the dissociation channels may be obtained directly from the C2H5+ images, yielding the quantum yield of I-* about 0.63-0.76, comparable to the case of CH3I. Anisotropy parameters (beta) determined for the I-* channel remain at 1.9 +/- 0.1 over the wavelength range studied, indicating that the I-* production should originate from the (3)Q(0) state. In contrast, the beta(I) values become smaller above 266 nm, comprising two components, direct excitation of (3)Q(1) and nonadiabatic transition between the (3)Q(0) and (1)Q(1) states. The curve crossing probabilities are determined to be 0.24-0.36, increasing with the wavelength. A heavier branched ethyl group does not significantly enhance the I(5p P-2(3/2)) production from the nonadiabatic contribution, as compared to the case of CH3I. (c) 2007 American Institute of Physics.