High-energy collisional activation of the molecular ions of thiophene-2-one with different target gases

Collisional activation of keV thiophene-2-one radical cations 1(+.) with O- 2 or NO. as the target gas leads to a desulfuration reaction. This peculiar reaction is insignificant or absent with other targets such as helium, arg on, methane or nitrogen. The radical cations produced in this desulfuration reaction are most probably vinylketene ions, as indicated by a triple mass spectrometric (MS/MS/MS) experiment performed on a 'hybrid' tandem mass sp ectrometer of sector-quadrupole-sector configuration. Tentatively, it is pr oposed that population of an excited state accounts for the non-ergodic beh avior of 1(+.) upon collision with oxygen or nitric oxide. Ab initio molecu lar orbital calculations using molecular orbital theory (UMP2, UCCSD(T)) an d density functional theory (B3LYP) with 6-31G(d,p) and 6-311++G(d,p) basis sets were used to evaluate the relative energy of the excited quartet stat e of 1(+.) radical cations. This quartet state is calculated to lie about 3 .6 eV above the (2)A " ground state and 0.9 eV above the C4H4O+. + S dissoc iation products. It is proposed that the quartet ion serves as the precurso r for the spontaneous desulfuration. Copyright (C) 2001 John Wiley & Sons, Ltd.