Mode-specific photoelectron scattering effects on CO2(+)(C2Sigmag+) vibrations.
Using high-resolution photoelectron spectroscopy, we have determined the energy dependent vibrational branching ratios for the symmetric stretch [v+ = (100)], bend [v+ = (010)], and antisymmetric stretch [v+ = (001)], as well as several overtones and combination bands in the 4sigmag(-1) photoionization of CO2. Data were acquired over the range from 20-110 eV, and this wide spectral coverage highlighted that alternative vibrational modes exhibit contrasting behavior, even over a range usually considered to be dominated by atomic effects. Alternative vibrational modes exhibit qualitatively distinct energy dependences, and this contrasting mode-specific behavior underscores the point that vibrationally resolved measurements reflect the sensitivity of the electron scattering dynamics to well-defined changes in molecular geometry. In particular, such energy-dependent studies help to elucidate the mechanism(s) responsible for populating the symmetry forbidden vibrational levels [i.e., v+ =( 010), (001), (030), and (110)]. This is the first study in which vibrationally resolved data have been acquired as a function of energy for all of the vibrational modes of a polyatomic system. Theoretical Schwinger variational calculations are used to interpret the experimental data, and they indicate that a 4sigmag-->ksigmau shape resonance is responsible for most of the excursions observed for the vibrational branching ratios. Generally, the energy dependent trends are reproduced well by theory, but a notable exception is the symmetric stretch vibrational branching ratio. The calculated results display a strong peak in the vibrational branching ratio while the experimental data show a pronounced minimum. This suggests an interference mechanism that is not accounted for in the single-channel adiabatic-nuclei calculations. Electronic branching ratios were also measured and compared to the vibrational branching ratios to assess the relative contributions of interchannel (i.e., Herzberg-Teller) versus intrachannel (i.e., photoelectron-mediated) coupling.
Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
G J
GJ
Rathbone
E D
ED
Poliakoff
John D
JD
Bozek
R R
RR
Lucchese
P
P
Lin
D002245:Carbon Dioxide / Q000737:chemistry* / Q000528:radiation effects*; D003198:Computer Simulation; D004583:Electrons; D007477:Ions / Q000737:chemistry / Q000528:radiation effects; D008027:Light; D008956:Models, Chemical; D008958:Models, Molecular; D010777:Photochemistry / Q000379:methods*; D011829:Radiation Dosage; D012542:Scattering, Radiation
D007477:Ions; D002245:Carbon Dioxide