Matrix isolation and ab initio study of the HXeCCHC O2 complex

Abstract

The HXeCCHC O2 complex is studied experimentally and computationally. The complex is prepared in a low-temperature xenon matrix using UV photolysis of propiolic acid (HCCCOOH) and thermal mobilization of H atoms at 45 K. Photolysis of propiolic acid leads to the HCCHC O2 complex as one of the photolysis products. The HCCHC O2 complex is further photolyzed to the HCCC O2 complex. Thermal annealing leads to the formation of HXeCCH complexed with C O2. The H-Xe stretching absorption of the HXeCCHC O2 complex is blueshifted (+31.9 and +5.8 cm-1) from the value of the HXeCCH monomer in a xenon matrix. In the calculations, three HXeCCHC O2 structures were found (one parallel and two linear structures) corresponding to the true energy minima on the potential energy surface. For the H-Xe stretching mode, the calculations give blueshifted values of +19.2 or +19.5 cm-1 depending on the computational level [MP26-311++G (2d,2p) and MP2/aug-cc-pVDZ] for the parallel structure and +19.4 or +27.9 cm-1 for one linear structure. For the second linear structure, the H-Xe stretching frequency is redshifted by -8.6 or -9.4 cm-1 at these levels of theory. Based on the calculations, the experimental band shifted by +5.8 cm-1 (1492.2 cm-1) most likely corresponds to the HXeCCHC O2 parallel structure. The band with larger blueshift of +31.9 cm-1 (1518.3 cm-1) can be due to another matrix site of the same structure or to the blueshifting linear structure. © 2007 American Institute of Physics.