Multiphoton ionization photoelectron spectroscopy of nitric oxide

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Abstract
We have investigated the photoelectron spectrum (PES) of nitric oxide following four-photon ionization resonant with various vibrational levels of the two-photon-allowed A state. The process studied was When the laser was tuned to each resonant vibrational state, two electron energy peaks were observed. For v = 0,1,2,3 the higher energy peak corresponds to direct ionization, leaving the positive ion in a single vibrational quantum state which is the same vibrational state as that of the initially excited nitric oxide Rydberg state. The origin of the lower energy peak representing near zero energy electrons is not understood at this time, but several possible mechanisms are discussed. The PES spectrum through the A2Σ+(v = 3) level indicates that two competing processes can occur—vibrational autoionization after three-photon absorption, or the ’’quasi-free–free’’ absorption of a fourth photon resulting in formation of the X 1Σ (v = 3) state of the ion. Results of multiphoton ionization PES resonant with the C state are also presented.