Scattering resonances in the rotational excitation of HDO by Ne and -H: theory and experiment.

The rotational excitation of a singly deuterated water molecule (HDO) by a heavy atom (Ne) and a light diatomic molecule (H) is investigated theoretically and experimentally in the near-threshold regime. Crossed-molecular-beam measurements with a variable crossing angle are compared to close-coupling calculations based on high-accuracy potential energy surfaces. The two lowest rotational transitions, 0 → 1 and 0 → 1, are probed in detail and a good agreement between theory and experiment is observed for both transitions in the case of HDO + Ne, where scattering resonances are however blurred out experimentally.

Near-Threshold and Resonance Effects in Rotationally Inelastic Scattering of DO with -H.

We present a combined experimental and theoretical study on the rotationally inelastic scattering of heavy water, DO, with -H. Crossed-molecular beam measurements are performed in the collision energy range between 10 and 100 cm, corresponding to the near-threshold regime in which scattering resonances are most pronounced. State-to-state excitation cross-sections are obtained by probing three low-lying rotational levels of DO using the REMPI technique.

Low-Energy Water-Hydrogen Inelastic Collisions.

New molecular beam scattering experiments are reported for the water-hydrogen system. Integral cross sections of the first rotational excitations of - and -HO by inelastic collisions with -H were determined by crossing a beam of HO seeded in He with a beam of H. HO and H were cooled in the supersonic expansion down to their lowest rotational levels.

Quantum Behavior of Spin-Orbit Inelastic Scattering of C-Atoms by D at Low Energy.

Fine-structure populations and collision-induced energy transfer in atoms are of interest for many fields, from combustion to astrophysics. In particular, neutral carbon atoms are known to play a role in interstellar media, either as probes of physical conditions (ground state P spin-orbit populations), or as cooling agent (collisional excitation followed by radiative decay). This work aims at investigating the spin-orbit excitation of atomic carbon in its ground electronic state due to collisions with molecular deuterium, an isotopic variant of H, the most abundant molecule in the interstellar medium.

Probing Nonadiabatic Effects in Low-Energy C( P ) + H Collisions.

Nonadiabatic effects are of fundamental interest in collision dynamics. In particular, inelastic collisions between open-shell atoms and molecules, such as the collisional excitation of C( P ) by H, are governed by nonadiabatic and spin-orbit couplings that are the sole responsible of collisional energy transfer. Here, we study collisions between carbon in its ground state C( P ) and molecular hydrogen (H) at low collision energies that result in spin-orbit excitation to C( P ) and C( P ).

Understanding the quantum nature of low-energy C(P ) + He inelastic collisions.

Inelastic collisions that occur between open-shell atoms and other atoms or molecules, and that promote a spin-orbit transition, involve multiple interaction potentials. They are non-adiabatic by nature and cannot be described within the Born-Oppenheimer approximation; in particular, their theoretical modelling becomes very challenging when the collision energies have values comparable to the spin-orbit splitting. Here we study inelastic collisions between carbon in its ground state C(P) and helium atoms-at collision energies in the vicinity of spin-orbit excitation thresholds (~0.

Variable-length cell for studies of gas spectra with extremely short optical paths.

We present a cell for studies of light transmission through very strongly absorbing gases. It uses a fixed window and a mirror, parallel to the latter and attached to a micrometric linear motion feedthrough monitoring mirror-window distances from 0 to a couple of centimeters. This device is tested by recording CO2 gas spectra near 4.

Low temperature rate coefficients for the reaction CN + HC3N.

The reaction of CN radicals with HC3N is of interest for interstellar and circumstellar chemistry as well as for the chemistry of Titan's atmosphere, as part of a general scheme for cyanopolyyne synthesis within these low temperature environments. Here, we present the first experimental measurements of its rate coefficient below room temperature down to 22 K, employing the CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme or Reaction Kinetics in Uniform Supersonic Flow) technique coupled with pulsed laser photolysis-laser-induced fluorescence. A novel pulsed version of the CRESU technique employing a new spinning disk valve was used for some of the kinetics measurements.

Experimental measurements of low temperature rate coefficients for neutral-neutral reactions of interest for atmospheric chemistry of Titan, Pluto and Triton: reactions of the CN radical.

The kinetics of the reactions of cyano radical, CN (X2sigma+) with three hydrocarbons, propane (CH3CH2CH3), propene (CH3CH=CH2) and 1-butyne (CH[triple band]CCH2CH3) have been studied over the temperature range of 23-298 K using a CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme or Reaction Kinetics in Uniform Supersonic Flow) apparatus combined with the pulsed laser photolysis-laser induced fluorescence technique. These reactions are of interest for the cold atmospheres of Titan, Pluto and Triton, as they might participate in the formation of nitrogen and carbon bearing molecules, including nitriles, that are thought to play an important role in the formation of hazes and biological molecules. All three reactions are rapid with rate coefficients in excess of 10(-10) cm3 molecule(-1) s(-1) at the lowest temperatures of this study and show behaviour characteristic of barrierless reactions.

A chemical dynamics, kinetics, and theoretical study on the reaction of the cyano radical (CN; X(2)Sigma+) with phenylacetylene (C6H5CCH; X(1)A1).

The chemical reaction dynamics to form o-, m-, and p-cyanophenylacetylene via the neutral-neutral reaction of ground state cyano radicals with phenylacetylene and D(1)-phenylacetylene were investigated in crossed beam experiments; these studies were combined with kinetics measurements of the rate coefficients at temperatures of 123, 200, and 298 K and supplemented by electronic structure calculations. The data suggest that the reaction is initiated by a barrier-less addition of the electrophilic cyano radical to the o-, m-, or p-position of the aromatic ring. The eventually fragmented via atomic hydrogen elimination to form o-, m-, and p-cyanophenylacetylene via tight exit transition states with the hydrogen atom being ejected almost perpendicularly to the molecular plane of the rotating complex.