The rotational spectrum of highly vibrationally mixed quantum states of propynol near 3330 cm−1

Abstract

The rotational spectra of molecular eigenstates of propynol in the region of the acetylenic C–H stretch (3330 cm−1) have been measured using infrared-microwave saturation spectroscopy. These spectra illustrate the basic properties of the rotational spectra of highly vibrationally mixed quantum states. From the measurements we are able to measure the average value of the rotational constant and the width of the rotational constant distribution. We determine that the average value of the quantity 12 (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 Gaussian. Narrowing of the rotational spectrum of single eigenstates by intramolecular vibrational energy redistribution (IVR) exchange processes is observed for the Ka=2 eigenstates. From the spectral narrowing we determine that the average IVR lifetime for vibrational states with Ka=2 near 3330 cm−1 is approximately 75 ps, about five times faster than the IVR lifetime of the Ka=2 states following coherent vibrational excitation of the acetylenic C–H stretch bright state (400 ps). Weak narrowing of the Ka=0 and Ka=1 eigenstates is observed below J=2. We estimate the IVR lifetime for Ka=0 and Ka=1 states as approximately 600 ps. The strong Ka dependence of the IVR rates of the bath states indicates that strong parallel Coriolis interactions play a primary role in the energy redistribution process.