Infrared Spectra of Gas-Phase V⁺−(Benzene) and V⁺−(Benzene)₂ Complexes

The organometallic ions V+−(benzene) and V+−(benzene)2 are produced by laser vaporization in a pulsed nozzle source. They are trapped and mass selected in an ion-trap/time-of-flight mass spectrometer, and their infrared spectra are measured with resonance-enhanced multiphoton photodissociation (IR-REMPD) spectroscopy with a tunable free-electron laser. Vibrational bands in the 600−1800 cm-1 region are characteristic of the benzene molecular moiety perturbed by the metal cation bonding. Experimental data are compared to the IR spectra derived from density functional calculations. Vibrational patterns in V+−(C6H6) indicate that the metal is bound in an η6 π-bonding configuration, while V+−(C6H6)2 is a sandwich. Trapped-ion IR-REMPD is a general method to access the vibrational spectroscopy of organometallic ions and their clusters