THE ROTATIONAL SPECTRUM OF HIGHLY VIBRATIONALLY MIXED QUANTUM STATES OF PROPYNOL NEAR 3330 CM(-1)

The rotational spectra of molecular eigenstates of propynol in the reg ion of the acetylenic C-H stretch (3330 cm(-1)) have been measured usi ng infrared-microwave saturation spectroscopy. These spectra illustrat e the basic properties of the rotational spectra of highly vibrational ly mixed quantum states. From the measurements we are able to measure the average value of the rotational constant and the width of the rota tional constant distribution. We determine that the average value of t he quantity 1/2 (B + C) is 17 MHz smaller than the,ground state value (a decrease of 0.4%). The width of the distribution (FHWM) is 90 MHz ( 1% of the ground state value). The distribution is approximately Gauss ian. Narrowing of the rotational spectrum of single eigenstates by int ramolecular vibrational energy redistribution (IVR) exchange processes is observed for the K-a = 2 eigenstates. From the spectral narrowing we determine that the average IVR lifetime for vibrational states with K-a = 2 near 3330 cm(-1) is approximately 75 ps, about five times fas ter than the IVR lifetime of the K-a = 2 states following coherent vib rational excitation of the acetylenic C-H stretch bright state (400 ps ). Weak narrowing of the K-a = 0 and K-a = 1 eigenstates is observed b elow J = 2. We estimate the IVR lifetime for K-a = 0 and K-a = 1 state s as approximately 600 ps. The strong K-a dependence of the IVR rates of the bath states indicates that strong parallel Coriolis interaction s play a primary role in the energy redistribution process. (C) 1998 A merican Institute of Physics.