Vacuum ultraviolet pulsed field ionization-photoelectron and infrared-photoinduced Rydberg ionization study of trans-1,3-butadiene

Abstract

The vacuum ultraviolet (VUV) laser pulsed field ionization-photoelectron (PFI-PE) spectrum of trans-1,3-butadiene (trans-CH2=CHCH=CH 2) has been measured in the region of 0-1700 cm-1 above its ionization energy (IE) to probe the vibrational modes vi+ (i=1-18) of trans-CH2=CHCH=CH2+. The high-frequency vibrational modes vi+ (i=19, 22, and 23) of trans-CH2=CHCH=CH2+ have also been probed by the VUV-infrared-photoinduced Rydberg ionization (VUV-IR-PIRI) measurement. On the basis of the semiempirical simulation of the origin VUV-PFI-PE band, the IE(trans-CH2=CHCH=CH2) is determined to be 73 150.1±1.5 cm-1 (9.06946±0.00019 eV). This value has been used to benchmark the state-of-the-art theoretical IE prediction based on the CCSD(T,Full)/CBS procedures, the calculation of which is reported in the present study. The vibrational bands observed in the VUV-PFI-PE and VUV-IR-PIRI spectra were assigned based on ab initio anharmonic vibrational frequencies and Franck-Condon factor calculations for the photoionization transitions. Combining the VUV-PFI-PE and VUV-IR-PIRI measurements, 17 fundamental vibrational frequencies of trans-CH2=CHCH=CH 2+ have been determined, including v1+ = 182±3, v2+ = 300±3, v 3+ = 428±3, v4+ = 514±3, v5+ = 554±5, v6+ = 901±3, v7+ = 928±5, v 8+ = 994±3, v9+ = 1008±5, v10+ = 1094±5, v13+ = 1258±3, v14+ = 1293±3, v 16+ = 1479±3, v18+ = 1620±3, v19+ = 2985±10, v22+ = 3030±10, and v23+ = 3105±10 cm-1. © 2008 American Institute of Physics.