Ultrafast resonance-enhanced multiphoton ionization in the azabenzenes: pyridine, pyridazine, pyrimidine, and pyrazine.
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 ~10(13) W/cm(2) to ~10(15) W/cm(2). 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-n)H(6-n)N(n)(+(+))) are observed with features suggesting resonance-enhanced ionization. From the intensity dependence of the ion yield, we infer that excitation occurs both through (1)ππ* transitions (remnants of the benzene structure) and through (1)nπ* transitions, the latter being a result of Rydberg-like excitations of the lone pair electrons of the nitrogen atoms. Stability against intense-field fragmentation is also discussed.
Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0299, USA. tim.scarborough@huskers.unl.edu
Timothy D
TD
Scarborough
David B
DB
Foote
Cornelis J G J
CJ
Uiterwaal
D007477:Ions; D008027:Light; D008958:Models, Molecular; D011719:Pyrazines / Q000737:chemistry*; D011724:Pyridazines / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*; D011743:Pyrimidines / Q000737:chemistry*
D007477:Ions; D011719:Pyrazines; D011724:Pyridazines; D011725:Pyridines; D011743:Pyrimidines; C062482:pyridazine; C030986:pyrimidine