Comparison of IRMPD, Ar-tagging and IRLAPS for vibrational spectroscopy of Ag+(CH3OH)

Gas-phase Ag+(CH3OH) molecules are produced in a laser ablation source, cooled in a supersonic expansion and their vibrational spectrum is measured by photofragment spectroscopy in a reflectron time-of-flight mass spectrometer. Three techniques - infrared multiple photon dissociation (IRMPD), argon-tagging, and infrared laser-assisted photodissociation spectroscopy (IRLAPS) - are used to measure the vibrational spectra of ions produced under identical conditions. The sharpest spectrum is obtained using IRLAPS, a two-color scheme in which a tunable OPO/OPA infrared laser excites the O-H stretch and a TEA-CO2 laser dissociates the vibrationally excited ions via absorbing multiple C-O stretch photons. The O-H stretch is observed at 3660 cm(-1). Monitoring loss of argon from Ag+(CH3OH)(Ar) gives a slightly broader peak, with no significant shift. The vibrational spectrum obtained using IRMPD is shifted to 3635 cm(-1) is substantially broader, and is asymmetrical, tailing to the red. Analysis of the experimental results is aided by comparison with hybrid density functional theory computed harmonic and anharmonic frequencies. (C) 2010 Elsevier B.A All rights reserved.