Electronic spectrum of the propargyl cation (H2C3H+) tagged with Ne and N2.

The Ã1A1 ← X...1A1 band system of the propargyl cation (H2C3H+) is measured over the 230-270 nm range by photodissociation of mass-selected H2C3H+-Ne and H2C3H+-N2 complexes in a tandem mass spectrometer. The band origin occurs at 37 618 cm-1 for H2C3H+-Ne and 37703 cm-1 for H2C3H+-N2. Ground and excited state ab initio calculations for H2C3H+ using the MCSCF and coupled-cluster (CC) response methods show that the ion has C2v symmetry in the ground X...1A1 and excited Ã1A1 states and that the strong vibronic progression with a spacing of 630 cm-1 is due to the C-C stretch vibrational mode, v5. [ABSTRACT FROM AUTHOR]