Vibrational overtone excitation followed by laserhyphen;induced fluorescence (LIF) interrogation determines statehyphen;tohyphen;state rotational and vibrational relaxation rates of highly energetic acetylene molecules by argon. We initially excite a single rotational state of the vibration 3ngr;3(three quanta of Cndash;H stretch,Evib=9640 cmminus;1) and detect the state (3ngr;3,Jf=20) in rotational relaxation measurements or the state (ngr;1+ngr;2+ngr;3+2ngr;4,l=0,Jf=4) in vibrational relaxation measurements. The data, which we acquire under singlehyphen;collision conditions, show that argon rotationally relaxes acetylene almost half as efficiently as acetylene itself but is relatively inefficient in vibrational relaxation. copy;1994 American Institute of Physics.
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