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Physical Review A

Vibrational quenching of N2(ν=1,jrot=j) by 3He: Surface and close-coupling calculations at very low energy

Thierry Stoecklin, A. Voronin, Jean Claude Rayez

Published Oct 3, 2002• 57 citations
Publisher

Abstract

A quantum-mechanical investigation of the vibrational deactivation of ${}^{14}{\mathrm{N}}_{2}(\ensuremath{\nu}=1,{j}_{\mathrm{rot}}=j)$ in the ultracold collisions with ${}^{3}\mathrm{He}$ atoms is presented. Ab initio potential-energy calculations are carried out at BCCD(T) level and a global three-dimensional potential-energy surface is obtained by fitting ab initio points within the reproducing kernel Hilbert space method. Close coupling scattering calculations are performed at collision energy ranging from ${10}^{\ensuremath{-}6}$ to 2000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. It is shown that the potential-energy surface supports a series of shape and Feshbach resonances. Their influence on the behavior of elastic and inelastic cross sections and quenching rate coefficients is discussed. It is demonstrated that, similar to the ${\mathrm{H}\mathrm{e}\ensuremath{-}\mathrm{O}}_{2}$ system, the rate coefficients exhibit three different regimes: Wigner regime at very low temperatures, van der Waals regime at intermediate temperatures due to series of resonances, and the usual rovibration--translation energy transfer regime at high temperatures.

DOI
10.1103/physreva.66.042703

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A quantum-mechanical investigation of the vibrational deactivation of 14N2(\ensuremathν=1,jrot=j){}^{14}{\mathrm{N}}_{2}(\ensuremath{\nu}=1,{j}_{\mathrm{rot}}=j)14N2​(\ensuremathν=1,jrot​=j) in the ultracold collisions with 3He{}^{3}\mathrm{He}3He atoms is presented. Ab initio potential-energy calculations are carried out at BCCD(T) level and a global three-dimensional potential-energy surface is obtained by fitting ab initio points within the reproducing kernel Hilbert space method. Close coupling scattering calculations are performed at collision energy ranging from 10\ensuremath−6{10}^{\ensuremath{-}6}10\ensuremath−6 to 2000 cm\ensuremath−1{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}cm\ensuremath−1. It is shown that the potential-energy surface supports a series of shape and Feshbach resonances. Their influence on the behavior of elastic and inelastic cross sections and quenching rate coefficients is discussed. It is demonstrated that, similar to the He\ensuremath−O2{\mathrm{H}\mathrm{e}\ensuremath{-}\mathrm{O}}_{2}He\ensuremath−O2​ system, the rate coefficients exhibit three different regimes: Wigner regime at very low temperatures, van der Waals regime at intermediate temperatures due to series of resonances, and the usual rovibration--translation energy transfer regime at high temperatures.
A comparative study of the vibrational deactivation of 14N2+^{14}\mathrm{N}_{2}^{+}14N2+​ ($\ensuremath{\nu}=1$, j=0j=0j=0) in collision with 3He^{3}\mathrm{He}3He and 4He^{4}\mathrm{He}4He atoms is investigated. Close-coupling calculations are carried out in the ${10}^{\ensuremath{-}6}--2000\text{\ensuremath{-}}{\mathrm{cm}}^{\ensuremath{-}1}$ kinetic energy range. At very low kinetic energy, it is found that the cross sections for the collision involving 3He^{3}\mathrm{He}3He is strongly enhanced by the presence of a virtual state associated with the van der Waals well. The change of mass from 3He^{3}\mathrm{He}3He to 4He^{4}\mathrm{He}4He also erases a strong shape resonance at $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ supported by the van der Waals well. As a result, the law of variation of the associated vibrational quenching rate coefficient is found to be very different for these two systems. This behavior is further analyzed by drawing the real part of the scattering length as a function of the variable mass of a fictitious He atom. Two zero energy resonances are identified for a mass of, respectively, about 3.18 and 3.85 atomic mass units.
Collisions of cold and ultracold BH in the ν = 0 level with the He atom are investigated using the quantum mechanical scattering formulation. The elastic and the inelastic cross sections are calculated using the two-dimensional ab initio potential energy surface. It is shown that the elastic cross section is larger than the inelastic one. When the collision energy is very low, the elastic cross section follows the Wigner threshold law and is one order of magnitude larger than that of He-O 2 , while it is much smaller than that of He-H 2 . The efficiency of the rotationally quenching state is given. The Δ j = −1 transition is most efficient. The resonances are also found to occur at about the same translational energy (0.1–1 cm −1 ), which gives rise to steps in the rate coefficient at temperatures around 0.1–1 K.
We present results of quantum mechanical scattering calculations including full rovibrational coupling on the relaxation of vibrationally excited H2{\mathrm{H}}_{2}H2​ molecules in collision with ultracold 3He{}^{3}\mathrm{He}3He and 4He{}^{4}\mathrm{He}4He atoms. The exothermic vibrational deactivation cross sections exhibit minima at translational temperatures near 10 K and show an inverse velocity dependence in accordance with Wigner's threshold law in the limit of zero kinetic energy. The corresponding rate coefficients exhibit minima before attaining constant values below ${10}^{\ensuremath{-}3}$ K. The rate coefficients increase by 3 orders of magnitude when the initial vibrational level of the molecule is raised from v=1v\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1v=1 to v=10v\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}10v=10. The results suggest that quasibound resonance states of 3HeH2{}^{3}{\mathrm{HeH}}_{2}3HeH2​ and 4HeH2{}^{4}{\mathrm{HeH}}_{2}4HeH2​ exist, associated with each excited vibrational state of H2{\mathrm{H}}_{2}H2​, and that both the triatomic species 3HeH2{}^{3}{\mathrm{HeH}}_{2}3HeH2​ and 4HeH2{}^{4}{\mathrm{HeH}}_{2}4HeH2​ have one bound vibrational state.
A new three-dimensional potential energy surface (PES), which describes the interaction between the OH(-)(X (1)Sigma(+)) anionic molecule and the Rb((2)S) atomic gas has been obtained by using a highly correlated ab initio model of the electronic structure and a large atomic basis set supplemented with a set of midbond Gaussian functions. This accurate PES is being employed to evaluate the OH(-)(X (1)Sigma(+)) vibrational quenching efficiency induced by collisions with Rb((2)S) at low and ultralow energies. Calculations employ the coupled-channel ansatz to describe the nuclear quantum dynamics and finally show a very marked dependence of the inelastic cross sections and rates, at vanishing collision energies, on the initial vibrational energy content of the partner molecules. The present findings allow us to make specific suggestions on the likely outcomes from energy interplay between the title species within a mixed MOT/Paul Trap environment.
We report quantum mechanical scattering calculations of zero temperature quenching rate coefficients for vibrationally and rotationally excited O 2 in collisions with 3 He. It is found that vibrational energy is channeled into more specific rotational levels in the ultracold regime than at thermal energies where a broad range of rotational levels are populated. The influence of the van der Waals interaction on the low-temperature quenching rate coefficients and the possibility of trapping vibrationally excited O 2 by the buffer gas cooling technique are also discussed.
We have developed a potential-energy surface for spin-polarized $\mathrm{K}(^{2}S)+{\mathrm{K}}_{2}(^{3}\ensuremath{\Sigma}_{u}^{+})$ collisions and carried out quantum dynamical calculations of vibrational quenching at low and ultralow collision energies for both bosons 39K^{39}\mathrm{K}39K and 41K^{41}\mathrm{K}41K and fermions 40K^{40}\mathrm{K}40K. At collision energies above about 0.1mK0.1\phantom{\rule{0.3em}{0ex}}\mathrm{mK}0.1mK the quenching rates are well described by a classical Langevin model, but at lower energies a fully quantal treatment is essential. We find that for the low initial vibrational state considered here (v=1)(v=1)(v=1), the ultracold quenching rates are not substantially suppressed for fermionic atoms. For both bosons and fermions, vibrational quenching is much faster than elastic scattering in the ultralow-temperature regime. This contrasts with the situation found experimentally for molecules formed via Feshbach resonances in very high vibrational states.