Abstract
We present an extensive range of accurate ab initio calculations, which map in detail the spatial electronic potential energy surface that describes the interaction between the molecular anion NH2- (1A1) in its ground electronic state and the He atom. The time-independent close-coupling method is employed to generate the corresponding rotationally inelastic cross sections, and then the state-changing rates over a range of temperatures from 10 to 30 K, which is expected to realistically represent the experimental trapping conditions for this ion in a radio frequency ion trap filled with helium buffer gas. The overall evolutionary kinetics of the rotational level population involving the molecular anion in the cold trap is also modelled during a photodetachment experiment and analyzed using the computed rates. The present results clearly indicate the possibility of selectively detecting differences in behavior between the ortho- and para-anions undergoing photodetachment in the trap.
Highlights
The outstanding progress which has been made in recent years in preparing atoms and molecules, neutral and ionized, into confined environments with temperatures down to the nanokelvin domain has allowed the making of a very versatile toolbox to the instrumentation for investigating atomic and molecular processes with neutral and ionized species
The 101 → 110 cross section increases as the collision energy drops until it reaches a maximum value above 20 cm 1 in contrast to the 000 → 111 cross section that uniformly decreases as the kinetic energy of the fragments decreases
We have investigated in this study a range of collisional energies and temperatures which are typical of ion trap experiments, i.e., in the temperature region between about 10 K and 30 K
Summary
The outstanding progress which has been made in recent years in preparing atoms and molecules, neutral and ionized, into confined environments with temperatures down to the nanokelvin domain has allowed the making of a very versatile toolbox to the instrumentation for investigating atomic and molecular processes with neutral and ionized species. One should further note the closeness of the structural values obtained by the present calculations and those provided by experiments.[11] Since both molecules are polar species, it is important in future photodetachment simulations to know the permanent dipole moment and the dipole orientation in the initial anionic partner. The orientation of the permanent dipole coincides with the direction of the unitary vector x (see Fig. 1) Another interesting piece of information obtainable from our calculations is linked to the spatial location of the bound excess electron in the negative ion since we already know that He atoms exhibit largely repulsive interactions with excess negative charges in the partner molecule. The extrapolations were carried out by including in the RKHS fitting the radial kernels of the forms q2,4, q2,5, and q2,6, respectively
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