Vacuum ultraviolet laser pulsed field ionization photoelectron study of <i>cis</i>-2-butene

Abstract

The vacuum ultraviolet pulsed field ionization-photoelectron spectra of supersonically cooled cis-2-butene (cis-CH3CH=CHCH3) have been measured in the photon energy range of 73 560–75 460 cm−1. Using the ab initio theoretical rotational constants of cis-CH3CH=CHCH3 and its cation (cis-CH3CH=CHCH3+) and a semiempirical simulation scheme, we have obtained a good fit of the origin vibrational band with partially resolved contours of rotational branches. After taking into account the Stark shift, the ionization energy of cis-CH3CH=CHCH3 is determined to be 73 595.0±1.5 cm−1. Guided by ab initio vibrational frequency calculations, we have also assigned the vibrational bands observed for cis-CH3CH=CHCH3+ in its ground state.