Determination of precise pyrimidine cationic structure by vacuum ultraviolet mass-analyzed threshold ionization spectroscopy

Abstract

The vibrational spectrum of a pyrimidine cation in the ground electronic state was obtained using vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy. Accurate ionization energy of pyrimidine was determined from the 0–0 band position in the VUV-MATI spectrum and was measured by varying the PFI field to the zero field limit, which is 75 258 ± 7 cm⁻¹ (9.3308 eV). The spectrum displayed a large number of vibrational peaks, which could be nearly completely assigned through Franck–Condon analysis performed with variations of geometrical parameters at the B3LYP/cc-pVTZ level. Based on the excellent agreement between experimental and calculated results, the definite geometry of the pyrimidine cation in the ground electronic state was determined to be a planar structure with C_2v symmetry with a decreased N–N distance in the ring.