Infrared Photodissociation Spectroscopy of Saturated Group IV (Ti, Zr, Hf) Metal Carbonyl Cations

Abstract

Group IV metal carbonyl cations of the form M(CO)n(+) (M = Ti, Zr, Hf; n = 6-8) are produced in a supersonic molecular beam via laser vaporization in a pulsed nozzle source. The ions are mass selected in a reflectron time-of-flight spectrometer and studied with infrared laser photodissociation spectroscopy in the carbonyl stretching region. The number of infrared active bands, their relative intensities, and their frequency positions provide insight into the structure and bonding of these complexes. Density functional theory calculations are employed to aid in the analysis of the experimental spectra. The n = 6 species is found to be the fully coordinated complex for each metal, and all analogues have a D3d structure. This symmetric structure and the resulting simple spectra facilitate the investigation of trends in the bonding and infrared band positions of these complexes. The carbonyl stretching frequencies of the M(CO)6(+) species are all red-shifted with respect to the gas phase CO vibration at 2143 cm(-1), occurring at 2110, 2094, and 2075 cm(-1) for titanium, zirconium and hafnium. The magnitude of the red shift increases systematically going from titanium to hafnium.