Photodissociation spectroscopy of the Ca+-C2H2 and Ca+-C2D2 π complexes

The Ca+-acetylene complex is produced in a molecular beam and studied with mass-selected resonance enhanced photodissociation spectroscopy (REPD). A spectrum with sharp vibrational and rotational structure is measured near the Ca+(P-2<--S-2) transition. Ca+-acetylene has a pi-complex structure with a ground slate vibrational frequency (Ca+-C2H2 stretch) of Delta G(1/2)"=169 cm(-1) and a dissociation energy of D-0"=18.6+/-5.0 kcal/mol. Isotopic studies performed show that Ca+-C2D2 has a ground state vibrational frequency (Ca+-C2H2 stretch) of Delta G(1/2)"=167 cm(-1). Excited state vibrational activity is observed in the metal-ligand stretch, the C-C and C-H stretches and the cis bend. The C-2 upsilon symmetry of the complex is confirmed with rotationally resolved spectra for both isotopomers, which yield a Ca+-C2H2 bond distance of r(0)"=2.80+/-0.20 Angstrom. (C) 1998 American Institute of Physics. [S0021-9606(98)01744-9].