PNNL

Abstract

The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. By using a high-resolution infrared (IR) laser to prepare propyne (C3H4) in selected rotational levels of the excited v1 (acetylenic C–H stretching) vibration mode prior to vacuum ultraviolet (VUV) laser pulsed field ionization-photoelectron (PFI-PE) measurements, we have obtained rotationally resolved VUV-PFI-PE spectra for the C3H4 +(X˜2E3/2,1/2 ,v1 +=1) band. The analysis of these PFI-PE spectra leads to the determination of the spin-orbit constant of A=-13.0±0.2 cm-1 for the C3H4 +(X˜ 2E3/2,1/2 ,v1 +=1) state. Using this A constant and the relative rotationally selected and resolved state-to-state photoionization cross sections thus measured, we have obtained an excellent simulation for the VUV-PFI-PE origin band of C3H4 +(X˜ 2E3/2,1/2), yielding a value of 83 619.0±1.0 cm-1 (10.367 44±0.000 12 eV) for the adiabatic ionization energy of C3H4 [IE(C3H4)]. The present two-color IR-VUV-PFI-PE study has also made possible the determination of the C–H stretching frequencies v1 +=3217.1±0.2 cm-1 for C3H4 +(X˜ 2E3/2,1/2). The spectral assignment and simulation were guided by high-level ab initio calculations on the IE(C3H4), Franck-Condon factors for photoionization transitions, and rotational constants and vibrational frequencies for C3H4 +.