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.

Three techniques – IRMPD, argon-tagging, and infrared laser-assisted photodissociation spectroscopy (IRLAPS) – are used to measure the vibrational spectra of Ag+(CH3OH) produced under identical conditions.Figure optionsDownload high-quality image (92 K)Download as PowerPoint slide