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Time-resolved infrared-ultraviolet double resonance (IR-UV DR) spectroscopy is used for examining the collision-induced kinetics of energy transfer in the 4[v.sub.CH] rovibrational manifold of acetylene ([C.sub.2][H.sub.2]). The master-equation model has included collision-induced energy transfer between discrete rovibrational levels in an IR-bright manifold and a quasi-continuous path, which is mediated by a J-specific gateway manifold.

Pulsed tunable infrared (IR) and ultraviolet (UV) lasers for time-resolved double-resonance (DR) spectroscopy is used to investigate the 4[nu.sub.CH] rovibrational manifold at 12 700 [cm.sup.-1] in the electronic ground state, X of acetylene ([C.sub.2][H.sub.2]). It results in a congested rovibrational manifold that exhibits complex intramolecular dynamics.

Collision-induced state-to-state molecular energy transfer between rovibrational states in the 12 700 cm(super -1) 4nu(sub CH) manifold of the electronic ground state of acetylene is monitored by time-resolved infrared-ultraviolet double resonance (IR-UV DR) spectroscopy. Three complementary forms of IR-UV DR experiments are used to address the extent to which intramolecular perturbations influence the efficiency of J-resolved collision-induced energy transfer with both even and odd delta J.

Time-resolved infrared-ultraviolet double resonance (IR-UV DR) spectroscopy is used to prepare acetylene molecules (C2H2) in specific rovibrational states. Three complementary forms of IR-UV DR experiment are reported that are IR-scanned, UV-scanned, and kinetic.

Vibrationally state-selected measurements of the kinetics and dynamics of 14N+2(v=1 and 2) and 15N+2(v=0, 1, and 2) in collisions with 14N2 are made using a selected ion flow tube (SIFT), laser induced fluorescence (LIF) technique at thermal energies. Kinetics are measured by monitoring the LIF signal amplitudes of N+2(v) as a function of 14N2 concentration, added after ion injection. By comparison with the known N+2(v=1)+Ar rate, the 15N+2(v=0)+14N2 rate constant is found to be one-half of the Langevin collision rate, or 4.2±0.2×10-10 cm3 molecule-1 s-1. This suggests that the reaction proceeds via an N+4 energized adduct in which charge is shared on a time scale shorter than the adduct lifetime. The removal rates of 14N+2(v=1 and 2) reactions by 14N2 are also found to proceed at one-half of the Langevin collision rate. Thus product channels that remove vibrational energy from the ion upon dissociation of the adduct account for 50% of the collision probability. The removal rates of 15N+2(v=1 and 2) with 14N2 are 21%–26% faster than those for 14N+2(v=1 and 2); this is attributed to the channel that cannot be observed in collisions of 14N+2(v) with 14N2 in which both charge and vibrational energy are transferred between the collision partners. This pathway is also observed directly by the appearance of 14N+2(v=1 and 2) product states. For this channel to proceed, vibrational energy transfer between the two highest frequency modes of the N+4 energized adduct must occur on a time scale comparable to the adduct lifetime. [ABSTRACT FROM AUTHOR]

An infrared–ultraviolet double resonance technique is used to probe the state-to-state rotational energy transfer dynamics of self-relaxation in acetylene. The output of an optical parametric oscillator at ∼3 μm is used to excite C2H2 to a rotational level within one of its Fermi-resonant 31,214151 states. By fixing this wavelength and scanning the frequency-doubled output of a tunable dye laser, laser induced fluorescence signals arising from collisional population of rotational levels within both dyads are observed and state-to-state rate constants for rotational relaxation are obtained. Rotational relaxation to J levels within the pumped (upper energy) Fermi-dyad accounts for 74% of the total rate of loss of the population of the J=12 level, whereas relaxation to J levels in its partner accounts for only 16%. A further 7% of the absolute rotational relaxation rate is accounted for by vibrational relaxation out of the mixed levels, leaving only 3%–4% of the total relaxation to be accounted for. [ABSTRACT FROM AUTHOR]

In this Communication, we report the use of a mass-selected flow tube, laser-induced fluorescence technique for the study of vibrationally excited ions. Using this technique, we have made measurements on the reaction of 15N2+ (v=2) with 14N2, which show conclusive evidence for the simultaneous transfer of vibrational energy and charge. We believe this to be the first direct observation of such a channel in charge transfer. [ABSTRACT FROM AUTHOR]