Rotational transitiosn of SO,SiO,and SiS excited by a discharge in a supersonic moleuclar beam:Vibrational temperatures,Dunham coefficients,Born-Oppenheimer breakdown,and hyperfine structure.

摘要

Fourier transform microwave spectroscopy has been used ot investigate vibrational excitation and relaxation of diatomic molecules produced by an electric discharge in the throat of a supersonic nozzle.Rotational transitions of SO,SiO,and SiS,in vibrational states up to v=33 for ~32S~16O,v=45 for ~28Si~16O,and v=51 for ~28Si~32S in their ground electronic states have bee detected.the isotopic species~33S~16O,~34S~16O,~29Si~16O,~28Si~18O,~29Si~32S,and ~28Si~34S have also been observed in highly excited vibrational states.Microwave transitions include up to v=22 for the second lowest excited electronic state b~1SIGMA~+of SO(approx 10510 cm~-1 above ground) have also been detected.Effective vibrational temperatures have ben derived for each species,and a general model is proposed ot qualitatively explain the observations.Vibrational excitation is caused by inelastic collisions withthe hot electrons produced in the discharge.The subsequent vibrational populations are largely determined byvibration-vibration energy transfer via molecule-moleucle binary collisions.Two regions can be inferred form the data:one characterizedby a temperature of around 1000 K adn a second region with a temperature of several thousand degrees Kelvin.Improved Dunham coefficients and correction terms for the breakdown fo the Born-Oppenheimer approximation have been determiend for b~1SIGMA~+ SO,X~1SIGMA~+ SiO,and X~1SIGMA~+ SiS.Nuclear spin-rotation hyperfine structure for the ~29Si isotopic species of SiO and SiS has been oberved in all highly excited vibrational states.