Infrared-ultraviolet double resonance spectroscopy of NO-Ne and NO-Ar complexes

Abstract

Van der Waals forces play an important role in the interaction at large molecular separation. It is responsible for the existence of liquid states. The interest in the van der Waals complexes originates from the prospect of understanding the transition from the gas phases to the condensed phases. Even though many van der Waals complexes involving closed-shell atoms and molecules have been studied, only few systems involving open-shell molecules have been studied. As a bench mark system for the interaction of an open shell molecule with a closed shell atom, a great focus has been on the NO-Ar system both experimentally and theoretically for the past two decades. The major source of experimental information on the interaction of NO with Ar relied on collision studies. So far, no spectroscopic information about the rovibrational levels of the electronic ground state of the NO-Ar complex is available. It is a goal of this dissertation to investigate the interaction potential of the electronic ground state of NO-Ar and NO-Ne complexes through IR spectroscopy. As a state specific detection scheme of molecules, (2+1) resonance enhanced multiphoton ionization(REMPI) has been used to the Rydberg state spectroscopy of van der Waals complexes, such as NO-Ar, NO-Ne, and CH3CHO-Ar. These studies provide information about the structure of the potential surface correlating with electronically excited NO. To explore the structure of the electronic ground state, REMPI detection was combined with IR spectroscopy. For the first time, observed are intermolecular vibration spectra of NO-Ar and NO-Ne built on the first overtone transition of NO. For both complexes, the agreement with Alexander's new results (J. Chem. Phys. 111,7435 (1999); J. Phys. Chem. 114, 5588 (2001)) based on his coupled-cluster (CCSD(T)) ab initio calculation of the two potential energy surfaces is excellent. Additional physical insight can be obtained by using a heuristic Hamiltonian based on perturbation theory. The results of this thesis opens new possibilities in exploring weak interactions involving van der Waals complexes using IR-REMPI double resonace technique.