Electric field effects in the near-threshold photoionization spectrum of nitric oxide

Abstract

Zero-kinetic-energy-photoelectron spectroscopy (ZEKE-PES) and time-of-flight mass spectrometry are used to investigate the near-threshold, two-color photoionization of NO via the A 2~+, v=O level. Pulsed-field ionization of Rydberg states within 20 cm-1 of the ionization threshold is shown to proceed via a diabatic mechanism. Particular emphasis is given to the effect of predissociation on the signal produced by delayed field ionization. A small ( -3 V / cm) dc electric field is shown to produce a dramatic decrease in the field ionization signal in both the NO+ -ion and ZEKE-electron channels. This decrease is thought to be due to an increase in the predissociation rate caused by the dc electric field. The implications of these experiments for mass-analyzed threshold ionization are discussed.

Decay of high Rydberg states: A paradigm for intramolecular dynamics in a congested bound level structure coupled to a continuum

“…The complementary aspect is that the scattering theory of unimolecular dissociation 8,9 enables us to provide insight on the question of the long lifetime of very high Rydberg states. [10][11][12][13][14][15][16][17][18][19] Much of the current discussion 13,18 -22 regards the lengthening of the lifetime of high Rydberg states to be primarily due to external electrical fields, which can be stray fields or can be the fields of neighboring species ͑primarily, ions which are excited, unavoidably 12 or intentionally 19,23 during the pumping of the Rydberg states͒. If that is the case, then the molecular nature of the ionic core is not central to the problem.…”

High Rydberg states of DABCO: Spectroscopy, ionization potential, and comparison with mass analyzed threshold ionization

“…The unexpected stability of these molecular Rydberg states as seen in ZEKE and MATI experiments 4,5,6 has led to a number of different models, 7,8,9 guided by the extensive work on atomic Rydberg states 10 and on simple diatomic systems. [11][12][13][14] Highly excited molecular Rydberg states of larger polyatomics have also been studied [15][16][17][18][19] but very few molecules show resolvable Rydberg progressions with principal quantum numbers nϾ50, which are the states probed by ZEKE/MATI. The highly symmetric caged amine DABCO ͑see Fig.…”

Zero kinetic energy-pulsed field ionization and resonance enhanced multiphoton ionization photoelectron spectroscopy: Ionization dynamics of Rydberg states in HBr

“…20 However, deviations from this value have been observed before. 21,22 Ionization thresholds were also measured for electric fields smaller than 25 V/cm but were found to be strongly nonlinear with respect to the square-root dependence. This nonlinearity is attributed mainly to the unknown contribution of stray fields, although contributions from collisional ionization under low field conditions may be also present.…”