Molecular-beam infrared-infrared double-resonance spectroscopy study of the vibrational dynamics of the acetylenic C-H stretch of propargyl amine

The acetylenic C-H stretch spectrum of propargyl amine near 3330 cm(-1) has been measured at 0.0002 cm(-1) (6 MHz) resolution with a tunable color-center laser in an electric-resonance optothermal spectrometer. The spectrum has been fully assigned through IR-IR double resonance measurements employing a tunable, microwave sideband-CO2 laser. The 10 mu m spectrum of propargyl amine displays splittings in the two nuclear spin symmetry states arising from amino-proton interchange, allowing double-resonance assignment of the -NH2 group resultant proton nuclear spin quantum number in the highly fragmented 3 mu m spectrum. The experimental state density is consistent with a (2J + 1) increase that is expected if all near-resonant states are coupled. From this J-dependent growth in the state density we determine the density of states at J = 0 to be 22 states/cm(-1). This value is in reasonable agreement with the direct state count result of 16 states/cm(-1). The unperturbed transition frequencies for the two different nuclear spin species at a given rotational level do not coincide, differing on average by about 50 MHz. The nonresonant coupling effects which produce effective splittings in the 10 mu m spectrum appear to survive into the high state density regime. The measured IVR lifetimes are on the order of 500 ps for the low K-a values studied here (K-a < 4) and show a K-a-dependence with the IVR rate increasing as K-a increases. The statistical properties of the spectrum have been compared to predictions from random matrix theory. The level spacings are not well represented by Wigner statistics as would be expected for underlying chaotic classical dynamics. However, the intensity fluctuations are consistent with a chi(2)-distribution, expected for classically chaotic systems, as measured by Heller's F-statistic. (C) 1998 American Institute of Physics.