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Register a new userRovibrational quenching of C$_2$-anions in collisions with He, Ne, and Ar atoms
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The dicarbon molecular anion is currently of interest as a candidate for laser cooling due to its electronic structure and favorable branching ratios to the ground electronic and vibrational states. Helium has been proposed as a buffer gas to cool the molecules internal motion. We calculate the cross sections and corresponding rates for rovibrational inelastic collisions of the dicarbon anion with He, and also with Ne and Ar, on three-dimensional ab initio potential energy surfaces using quantum scattering theory. The rates for vibrational quenching with He and Ne are very small and are similar to those for small neutral molecules in collision with helium. The quenching rates for Ar, however, are far larger than those with the other noble gases, suggesting that this may be a more suitable gas for driving vibrational quenching in traps. The implications of these results for laser cooling of the dicarbon anion are discussed.
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The vibrational quenching cross sections and corresponding low-temperature rate constants for the v = 1 and v = 2 states of CN- colliding with He and Ar atoms have been computed ab initio using new three dimensional potential energy surfaces. Little work has so far been carried out on low-energy vibrationally inelastic collisions for anions with neutral atoms. The cross sections and rates calculated at energies and temperatures relevant for both ion traps and astrochemical modelling, are found by the present calculations to be even smaller than those of the similar C2- /He and C2-/Ar systems which are in turn of the order of those existing for the collisions involving neutral diatom-atom systems. The implications of our finding in the present case rather small computed rate constants are discussed for their possible role in the dynamics of molecular cooling and in the evolution of astrochemical modelling networks.
We report on a direct method to measure the internuclear potential energy curve of diatomic systems. A COLTRIMS reaction microscope was used to measure the squares of the vibrational wave functions of H$_{2}$, He$_{2}$, Ne$_{2}$, and Ar$_{2}$. The Schrodinger equation relates the curvature of the wave function to the potential V(R) and therefore offers a simple but elegant way to extract the shape of the potential.
Electron removal in collisions of alpha particles with neon dimers is studied using an independent-atom-independent-electron model based on the semiclassical approximation of heavy-particle collision physics. The dimer is assumed to be frozen at its equilibrium bond length and collision events for the two ion-atom subsystems are combined in an impact parameter by impact parameter fashion for three mutually perpendicular orientations. Both frozen atomic target and dynamic response model calculations are carried out using the coupled-channel two-center basis generator method. We pay particular attention to inner-valence Ne($2s$) electron removal, which is associated with interatomic Coulombic decay (ICD), resulting in low-energy electron emission and dimer fragmentation. Our calculations confirm a previous experimental result at 150 keV/amu impact energy regarding the relative strength of ICD compared to direct electron emission. They further indicate that ICD is the dominant Ne$^+$ + Ne$^+$ fragmentation process below 10 keV/amu, suggesting that a strong low-energy electron yield will be observed in the ion-dimer system in a regime in which the creation of continuum electrons is a rare event in the ion-atom problem.
We present an experimental study on the rotational inelastic scattering of OH ($X^2Pi_{3/2}, J=3/2, f$) radicals with He and D$_2$ at collision energies between 100 and 500 cm$^{-1}$ in a crossed beam experiment. The OH radicals are state selected and velocity tuned using a Stark decelerator. Relative parity-resolved state-to-state inelastic scattering cross sections are accurately determined. These experiments complement recent low-energy collision studies between trapped OH radicals and beams of He and D$_2$ that are sensitive to the total (elastic and inelastic) cross sections (Sawyer emph{et al.}, emph{Phys. Rev. Lett.} textbf{2008}, emph{101}, 203203), but for which the measured cross sections could not be reproduced by theoretical calculations (Pavlovic emph{et al.}, emph{J. Phys. Chem. A} textbf{2009}, emph{113}, 14670). For the OH-He system, our experiments validate the inelastic cross sections determined from rigorous quantum calculations.
In this work we discuss the rotational structure of Rydberg molecules. We calculate the complete wave function in a laboratory fixed frame and derive the transition matrix elements for the pho- toassociation of free ground state atoms. We discuss the implications for the excitation of different rotational states as well as the shape of the angular nuclear wave function. We find a rather com- plex shape and unintuitive coupling strengths, depending on the angular momenta coupling that are relevant for the states. This work explains the different steps to calculate the wave functions and the transition matrix elements in a way, that they can be directly transferred to different molecular states, atomic species or molecular coupling cases.
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