Ultrafast resonance-enhanced multiphoton ionization in the azabenzenes: Pyridine, pyridazine, pyrimidine, and pyrazine

Authors

• Timothy D. Scarborough, University of Nebraska-LincolnFollow
• David B. Foote,, University of Nebraska-Lincoln
• Cornelis J. Uiterwaal, University of Nebraska - LincolnFollow

Document Type

Article

Date of this Version

2012

Citation

THE JOURNAL OF CHEMICAL PHYSICS 136, 054309 (2012); doi:10.1063/1.3682541

Comments

Copyright 2012 American Institute of Physics

Abstract

We report on the ultrafast photoionization of pyridine, pyridazine, pyrimidine, and pyrazine. These four molecules represent a systematic series of perturbations into the structure of a benzene ring which explores the substitution of a C–H entity with a nitrogen atom, creating a heterocyclic structure. Data are recorded under intense-field, single-molecule conditions. The pulses (50 fs, 800 nm) are focused into the molecular vapor, and ion mass spectra are recorded for intensities of ∼10¹³ W/cm² to ∼10¹⁵ W/cm². We measure ion yields in the absence of the focal volume effect without the need for deconvolution of the data. For all targets, stable singly- and doubly-charged parent ions (C_6-nH_6-nN_n ⁺⁽⁺⁾) are observed with features suggesting resonance-enhanced ionization. From the intensity dependence of the ion yield, we infer that excitation occurs both through 1ππ* transitions (remnants of the benzene structure) and through ¹nπ^* transitions, the latter being a result of Rydberg-like excitations of the lone pair electrons of the nitrogen atoms. Stability against intensefield fragmentation is also discussed.