Influence of vibrational excitation and collision energy on the ion‐molecule reaction NH+3(ν2)+ND3

Mode selective tunneling dynamics observed by high resolution spectroscopy of the bending fundamentals of N14H2D and N14D2H

High resolution (0.004 and 0.01 cm(-1) instrumental bandwidth) interferometric Fourier transform infrared spectra of (14)NH2D and (14)ND2H were measured on a Bomem DA002 spectrometer in a supersonic jet expansion and at room temperature. We report the analysis of the bending fundamentals of (14)NH2D with term values Tv(s)=1389.9063(2) cm(-1) and Tv(a)=1390.4953(2) cm(-1) for the nu(4b) fundamental and Tv(s)=1605.6404(7) cm(-1) and Tv(a)=1591.0019(7) cm(-1) for the nu(4a) fundamental, and of (14)ND2H with term values of Tv(s)=1233.3740(2) cm(-1) and Tv(a)=1235.8904(2) cm(-1) for the nu(4a) fundamental and Tv(s)=1461.7941(9) cm(-1) and Tv(a)=1461.9918(19) cm(-1) for the nu(4b) fundamental. In all cases Tv(s) gives the position of the symmetric inversion sublevel (with positive parity) and Tv(a) the position of the antisymmetric inversion sublevel (with negative parity). The notation for the fundamentals nu(4a) and nu(4b) is chosen by correlation with the degenerate nu(4) mode in the C(3v) symmetric molecules NH3 and ND3. The degeneracy is lifted in Cs symmetry and a indicates the symmetric, b the antisymmetric normal mode with respect to the Cs symmetry plane in NH2D and ND2H. Assignments were established with certainty by means of ground state combination differences. About 20 molecular parameters of the effective S-reduced Hamiltonian could be determined accurately for each fundamental. In particular, the effect of Fermi resonances of the 2nu(2) overtone with the nu(4a) bending mode was observed, leading to an increased inversion splitting in the case of ND2H and to a strongly increased inversion splitting and an inverted order of the two inversion levels in NH2D. Rotational perturbations observed with the nu(4b) bending fundamentals are probably due to Coriolis interactions with the inversion overtone 2nu(2). The results are important for understanding isotope effects on the inversion in ammonia as well as its selective catalysis and inhibition by excitation of different vibrational modes, as treated by quantum dynamics on high dimensional potential hypersurfaces of this molecule.

Theoretical study of the hydrogen atom transfer in the heterodimer indole-ammonia and comparison with experimental results

Ab initio calculations on the heterodimer C8H6NH...NH3 are carried out for its ground, the excited pisigma*, and the ground cationic electronic states, enabling the description of hydrogen or proton transfer, respectively. Two-dimensional quantum-dynamical computations on the pisigma* potential surface help one to understand the mechanism and the time scale of the hydrogen transfer. Subsequent decay processes are discussed depending on the vibrational excitation of the ammonium constituent. Finally, the theoretical results obtained are used for the interpretation of the time-dependent signals observed in femtosecond pump-probe experiments.

Intramolecular Vibrational Dynamics of the Asymmetric &dbond;CH2 Hydride Stretch of Isobutene

The eigenstate-resolved, high-resolution (5 MHz) infrared spectrum of the asymmetric &dbond;CH2 hydride stretch of isobutene has been measured using an electric resonance optothermal spectrometer (EROS). This vibrational band near 3087 cm-1 was rotationally assigned with ground state microwave-infrared double-resonance spectroscopy. IVR rates from rotationally homogeneous IVR multiplets at values of total angular momentum, J ranging from J = 0 to J = 3 and Ka values of Ka = 0 to Ka = 2, were obtained. The average IVR lifetime for this vibrational mode is 105 ps and independent of rotational state. The experimental state density of the rotationless 000 vibrational state, approximately 150 states/cm-1, is in good agreement with the direct count result of 99 states/cm-1 using the C+3 v multiply sign in circle C-3 v (G36) molecular symmetry group. The lineshape profiles of the IVR multiplets are investigated in order to elucidate information concerning the dependence of IVR rates on the symmetry of the torsional wavefunction. We find that there is a common IVR rate among the various torsional symmetries. IVR lifetimes observed in the present study are compared to other asymmetric ethylenic hydride stretch IVR rates measured in our laboratory. Copyright 1999 Academic Press.

Partial Control of an Ion-Molecule Reaction by Selection of the Internal Motion of the Polyatomic Reagent Ion

The ion-molecule reaction NH(3)(+) + ND(3) has been studied at various collision energies (1 to 5 electron volts in the center of mass) with preparation of the NH(3)(+) reagent in two nearly isoenergetic vibrational states. One state corresponds to pure out-of-plane bending of the planar NH(3)(+) ion (0.60 electron volts), whereas the other state is a combination of in-plane and out-of-plane motion (0.63 electron volts). The product branching ratios differ markedly for these two vibrational-state preparations. The differences in reactivity suggest that the in-plane totally symmetric stretching mode is essentially inactive in controlling the branching ratio of this reaction.