The QOQ (quadrupole-octupole-quadrupole) experiment is designed to measure vibrational transitions of gas phase ions and clusters by a method of action spectroscopy referred to as infrared photodissociation (IRPD) spectroscopy. In this technique, the molecules of interest are tagged by weakly bound ligands (e.g. Argon) that detach from the ions upon vibrational excitation (tagging spectroscopy). The experiment consists of a tandem quadrupole mass spectrometer and an octopole ion guide coupled to an electron ionization cluster ion source. The clusters are produced in a pulsed supersonic plasma expansion by electron and/or chemical ionization followed by three-body aggregation reactions . Mass selected clusters (parent) are irradiated with a tuneable IR laser pulse of a tunable optical parametric oscillator pumped by a Q-switched nanosecond Nd:YAG laser. The laser setup allows measurements over a wavenumber range of 600 to 4000 cm-1. Resonant vibrational excitation upon single photon absorption leads to evaporation of a single ligand. The resulting fragment ions (daughter) are selected by the second quadrupole and monitored by a Daly detector as a function of the laser frequency to obtain infrared photodissociation (IRPD) spectra. IRPD spectroscopy and quantum chemical calculations can be used to characterize the structural, vibrational, and energetic properties of ions and their clusters.
Biomolecules, protonated aromatic molecules, diamondoids, silicion hydrides