Eigenstate resolved infrared/infrared double resonance spectroscopy of the 3ν1 overtone band of 1-propyne: Intramolecular vibrational energy redistribution into a Coriolis-coupled bath

Abstract

Sequential infrared/infrared double resonance excitation of an optothermally detected molecular beam has been used to obtain the eigenstate resolved spectrum of the second C–H stretch overtone in propyne near 9700 cm⁻¹. The high resolution and sensitivity of this technique allows for extraction of detailed information about the dynamics of intramolecular vibrational energy redistribution from this highly fractionated spectrum. The analysis suggests a coupling mechanism consisting of anharmonic coupling out of the bright state through a doorway state or first tier, followed by subsequent coupling to a strongly Coriolis mixed bath. The lifetime of the bright state, which is determined by the first step and is not dependent on the total angular momentum, is measured to be about 320 ps for the K=0 clumps and about 210 ps for the K=1 clumps. The root mean square coupling matrix element determined for the J’=0 clump is 0.008 cm⁻¹ and decreases with increasing J’. According to the level spacing and Heller’s F statistics, the spectrum shows evidence indicating that the underlying dynamic behavior is chaotic.