Shape and strength of dynamical couplings between vibrational levels of the H2 +, HD+ and D2 + molecular ions in collision with He as a buffer gas

Abstract

Abstract. We present a detailed computational analysis for the interaction between the vibrating/rotating molecular ions H + 2 , HD + , D + 2 colliding with He atoms employed as buffer gas within ion trap experiments. The production and preparation of these molecular ions from their neutrals usually generate rovibrationally excited species which will therefore require internal energy cooling down to their ground vibrational levels for further experimental handling. In this work we describe the calculation of the full 3D interaction potentials and of the ionic vibrational levels needed to obtain the vibrational coupling potential matrix elements which are needed in the multichannel treatment of the rovibrationally inelastic collision dynamics. The general features of such coupling potential terms are discussed for their employment within a quantum dynamical modeling of the relaxation processes, as well as in connection with their dependence on the initial and final vibrational levels which are directly coupled by the present potentials. As a preliminary test of the potential effects on scattering observables, we perform calculations between H + 2 and He atoms at the energies of an ion-trap by using either the rigid rotor (RR) approximation or the more accurate vibrationally averaged (VA) description for the v = 0 state of the target. Both schemes are described in detail in the present paper and the differences found in the scattering results are also analysed and discussed. We further present and briefly discuss some examples of state-to-state rovibrationally inelastic cross sections, involving the two lowest vibrational levels of the H + 2 molecular target ion, as obtained from our time-independent multichannel quantum scattering code.

Rotationally inelastic cross sections, rates and cooling times for para-H2 +, ortho-D2 + and HD+ in cold helium gas

“…All the details of the expansion of equation (1) were extensively discussed and analyzed in reference [13] and will not be repeated here. We have also carried out a detailed comparison of our present choice for the non-reactive PES with additional earlier calculations (which turned out to be very similar to our present choice) in another, separate publication from our group [17]. Suffice it to say that our present choice of the interaction potential agrees closely with all the most recent evaluations of the same PES and indicates the accurate quality of the description of it which we have employed in the present work.…”

“…One clearly sees that the mass difference between the proton and deuteron causes an asymmetry in the two systems show instead the expected symmetry on the two sides of approach, not shown in this work but discussed elsewhere [17] in greater detail.…”

“…The two-dimensional PES was obtained from the full three-dimensional PES by averaging over the intermolecular ground-state vibrational wavefunction, a procedure we had previously called the Vibrationally Averaged (VA) final interaction potential for the case of the target's ground vibrational state. For further details see again reference [17] that reports our detailed comparison of the most recent PESs for the present MHI targets.…”

Rovibrational quenching of C2− anions in collisions with He, Ne, and Ar atoms

“…The differences between the VA and RR cross sections obtained using the present PES are small, as is expected since the ν = 0 vibrational wave function is strongly peaked around r = r eq . This behavior was also found for H 2 + -He collisions [77] and justifies our previous treatment of the molecule as a rigid rotor. From Fig.…”

Dynamics of systems on the nanoscale

“…A computational analysis for the interaction between the vibrating/rotating molecular ions H colliding with He atoms is presented in reference [13]. The work describes the calculation of the 3D interaction potentials and of the ionic vibrational levels needed to obtain the vibrational coupling potential matrix elements which are needed in the multichannel treatment of the rovibrationally inelastic collision dynamics.…”