Isotopically selective IR multiphoton dissociation of SF 6 in a pulsed gas dynamic flow interacting with solid surface

Abstract

When a pulsed gas dynamically cooled supersonic molecular flow interacts with solid surface a pressure shock is formed in front of it, non-equilibrium conditions in which may be inverse to those in the incident (unperturbed) flow ( T 1,tr⩽ T 1,rot⩽ T 1,vib in the incident flow and T 2,tr⩾ T 2,rot⩾ T 2,vib in the pressure shock; T i, tr , T i, rot and T i,vib are the translational, the rotational and the vibrational temperatures of molecules accordingly). Isotopically selective IR multiphoton dissociation of SF 6 (i) in the non-equilibrium conditions of the pressure shock, (ii) in the flow incident on the surface, and (iii) in an unperturbed flow was investigated. The parameters of the molecular flow and the conditions of formation of the pressure shock were studied. The time-of-flight spectra of SF 6 in the flow interacting with surface were obtained. The dissociation yield of SF 6 versus the excitation laser energy and frequency in the flow interacting with surface was investigated. The SF 4 product yield and the selectivity of SF 6 dissociation were measured. It is shown, that the efficiency of isotopically selective dissociation of molecules in the pulsed gas dynamic flow can be essentially increased at the expense of formation of a pressure shock in the front of the surface. The concentration and temperature of SF 6 in the pressure shock are estimated and the obtained results are discussed.