Pulsed field ionization threshold photoelectron spectroscopy with coherent vacuum ultraviolet: NO+(a 3Σ+ v=0,1,2)←NO(X 2Π1/2)

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Abstract
We report pulsed field ionizationspectra of an ionic electronically excited state, specifically, the NO+(a 3Σ+ v +=0,1,2)←NO(X 2Π1/2) transition. A coherent vacuum ultraviolet lightsource provides single photon excitation, which enables a direct measurement of the ionization potentials for the three vibrational levels — I.P.(v +=0)=126 392±1.5 cm−1, I.P.(v +=1)=127 653±1.5 cm−1, and I.P.(v +=2)=128 884±1.5 cm−1. The rotational structure of these spectra has been simulated using a standard model for rotational line strengths in a photoelectron spectrum, and this simulation shows the strong atomic p orbital character of the initial NO orbital from which the electron is photoionized. However, our data show that the rotational line strengths are strongly dependent on the final vibrational state of NO+, in disagreement with the theoretical model. Also, the spectrum for the v +=1 state of NO+ is strongly affected by the presence of a strong autoionizing Rydberg resonance at the same photon energy, which leads to a complex resonance.