(1+1) Resonant Enhanced Multiphoton Ionization via the A 2 Sigma + State of NO: Ionic Rotational Branching Ratios and Their Intensity Dependence
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Recent high resolution photoelectron spectroscopic studies of the (1+1) resonant enhanced multiphoton ionization (REMPI) of NO via the 0-0 transition of the A-X bond (gamma band) have shown a pronounced Delta N = 0 signal Delta N = N sub (+) - N sub i and smaller, but measurable, Delta N = + or - 2 peaks. The excitation was assigned to be via an R (21.5) line, with no further specification. Ab initio calculations of the rotational branching ratios are performed for the four possible R(21.5) transitions, namely, the rotationally clean R21 and R22, nd the mixed R12 + Q22 and R11 + Q21 branches. We find the mixed R12 + Q22(21.5) branch to agree best with the observed photoelectron spectrum collected parallel to the polarization vector of the light. The discrepancy is larger for detection perpendicular to the polarization. To understand this difference, we have assessed the influence of laser intensity and polarization contamination on the branching ratios and photoelectron angular distributions. Reprints. (jhd)