Abstract:The OCS photodissociation dynamics of the dominant S( 1 D 2 ) channel near 214 nm have been studied using velocity map ion imaging. We report a CO vibrational branching ratio of 0.79:0.21 for v=0:v=1, indicating substantially higher vibrational excitation than that observed at slightly longer wavelengths. The CO rotational distribution is bimodal for both v=0 and v=1, although the bimodality is less pronounced than at longer wavelengths. Vector correlations, including rotational alignment, indicate that absorption to both the 2 1

We present analytical expressions for extracting Dixon's bipolar moments in the semi-classical limit from experimental anisotropy parameters of sliced or reconstructed non-sliced images. The current method focuses on images generated by 2 + 1 REMPI (Resonance Enhanced Multi-photon Ionization) and is a necessary extension of our previously published 1 + 1 REMPI equations. Two approaches for applying the new equations, direct inversion and forward convolution, are presented. As demonstration of the new method, bipolar moments were extracted from images of carbonyl sulfide (OCS) photodissociation at 230 nm and NO photodissociation at 355 nm, and the results are consistent with previous publications.

We report on one-color experiments near 214 nm involving the photodissociation of jet-cooled OCS to produce high rotational states (40 < J < 80) of CO (X 1Σ+, v = 0, 1) which were then ionized by 2+1 resonance-enhanced multiphoton ionization via the E 1Π state. The nominally forbidden Q-branch of the two-photon E 1Π–X 1Σ+ transition is observed with intensity comparable to the allowed R-branch. The bright character of the high-J Q-branch lines can be described quantitatively as intensity borrowing due to mixing of the E 1Π and C 1Σ+ states, using J-dependent mixing coefficients extrapolated from the observed Λ-doubling in the lower rotational levels of the E state. In addition to the significant enhancement of Q-branch intensities above the values predicted by conventional two-photon line strengths for a 1Π–1Σ+ transition, the high-J lines of the R- and P-branches appear to be suppressed in intensity by approximately a factor of 3 compared to the unperturbed low-J line strengths, most likely due to perturbations associated with a 1Σ– state. The E-state rotational term values for J < 80, v = 0 derived from the present spectra agree within our measurement and calibration uncertainties with the extrapolations based on the molecular constants previously derived from rotational levels with J < 50. The E–X transition is attractive for future application to photodissociation dynamics and rotational polarization measurements of CO photofragments, with convenient access to state-selective probing on multiple rotational branches, which exhibit different sensitivity to fragment alignment.

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