Threshold Photoelectron Spectroscopy of Cyclopropenylidene, Chlorocyclopropenylidene, and Their Deuterated Isotopomeres

Cyclopropenylidene (c-C3H2), chlorocyclopropenylidene (c-C3HCl), and their deuterated isotopomers were studied by the threshold photoelectron-photoion coincidence (TPEPICO) technique using VUV synchrotron radiation. The carbenes were generated via flash pyrolysis. In all species a change in geometry is visible upon ionization, with significant activity in the C=C, C-C-stretching mode and, in the case of c-C3H2/D-2, the C-H-bending mode. The electron is removed from an sp(2) like hybrid orbital centered on the carbene C atom. The mass selected threshold photoelectron (TPE) spectra were fitted by a Franck-Condon simulation, yielding the equilibrium geometry of the cation ground state ((1)A(1)). The adiabatic ionization energy IEad of c-C3H, was determined to be 9.17 eV, in good agreement with calculations and literature values. Two vibrational wavenumbers of the cation were determined experimentally (nu(+)(3) = 1150 cm(-1) and nu(+)(2) = 1530 cm(-1)). Chlorocyclopropenylidene was also studied by TPE spectroscopy and has a similar IEad of 9.17 eV. The spectrum also shows a vibrational progression that corresponds to the C=C- and C-C-stretching modes of the cation. The equilibrium geometry was also determined by a Franck-Condon fit. The IEad of the deuterated isotopomers, c-C3D2 and c-C3DCl, were also determined to be 9.17 eV. The spectra confirm the assignments for the nondeuterated species.