Conformation-specific dissociative photoionization of oxalyl chloride in the gas phase

Abstract

The photoionization and photodissociation of oxalyl chloride have been studied by synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry. The ionization energy of C2Cl2O2 (10.91±0.05eV) and appearance energies (AEs) for fragment ions CCl2O+, C2ClO2+, CClO+, C2O2+, CO2+, and Cl+ from C2Cl2O2 have been measured from the photoionization efficiency (PIE) spectra. In addition, three conformers of C2Cl2O2+ ion, namely trans-, gauche- and cis-conformer are investigated by using CBS-QB3 and W1u methods, which suggest that the existence of the cis-conformation parent ion C2Cl2O2+ is consistent with the second onset at 11.6eV in the experimental PIE curve and the associated calculations. The formation channels of fragment ions near the ionization thresholds are discussed by means of CBS-QB3 and W1u calculated results and thermochemistry results. The dominant fragment ion CClO+ is mainly originated from direct cleavage of the elongated C–C bond in the trans-conformer parent ion after ionization. The calculated results are in good agreement with the experimental data.