MOLECULAR-BEAM INFRARED-INFRARED DOUBLE-RESONANCE SPECTROSCOPY STUDY OF THE VIBRATIONAL DYNAMICS OF THE ACETYLENIC C-H STRETCH OF PROPARGYLAMINE

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 m easurements employing a tunable, microwave sideband-CO2 laser. The 10 mu m spectrum of propargyl amine displays splittings in the two nuclea r spin symmetry states arising from amino-proton interchange, allowing double-resonance assignment of the -NH2 group resultant proton nuclea r spin quantum number in the highly fragmented 3 mu m spectrum. The ex perimental state density is consistent with a (2J + 1) increase that i s expected if all near-resonant states are coupled. From this J-depend ent 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 wi th 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 spli ttings in the 10 mu m spectrum appear to survive into the high state d ensity regime. The measured IVR lifetimes are on the order of 500 ps f or 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 proper ties of the spectrum have been compared to predictions from random mat rix theory. The level spacings are not well represented by Wigner stat istics as would be expected for underlying chaotic classical dynamics. However, the intensity fluctuations are consistent with a chi(2)-dist ribution, expected for classically chaotic systems, as measured by Hel ler's F-statistic. (C) 1998 American Institute of Physics.