State Specific Stabilization of H⁺ + H₂(j) Collision Complexes

Abstract

Stabilization of H3(+) collision complexes has been studied at nominal temperatures between 11 and 33 K using a 22-pole radio frequency (rf) ion trap. Apparent binary rate coefficients, k(*) = kr + k3[H2], have been measured for para- and normal-hydrogen at number densities between some 10(11) and 10(14) cm(-3). The state specific rate coefficients extracted for radiative stabilization, kr(T;j), are all below 2 × 10(-16) cm(3) s(-1). There is a slight tendency to decrease with increasing temperature. In contrast to simple expectations, kr(11 K;j) is for j = 0 a factor of 2 smaller than for j = 1. The ternary rate coefficients for p-H2 show a rather steep T-dependence; however, they are increasing with temperature. The state specific ternary rate coefficients, k3(T;j), measured for j = 0 and derived for j = 1 from measurements with n-H2, differ by an order of magnitude. Most of these surprising observations are in disagreement with predictions from standard association models, which are based on statistical assumptions and the separation of complex formation and competition between stabilization and decay. Most probably, the unexpected collision dynamics are due to the fact that, at the low translational energies of the present experiment, only a small number of partial waves participate. This should make exact quantum mechanical calculations of kr feasible. More complex is three-body stabilization, because it occurs on the H5(+) potential energy surface.

Dynamics of the D+ + H2 → HD + H+ reaction at the low energy regime by means of a statistical quantum method

“…14 The observed resonances observed here and for the scattering reactions for the H + 3 system 4 can be directly related with H + −H 2 radiative association processes. 44,60 In recent experimental radio frequency ion trap investigations, the deviations from the expected statistical behaviour were tentatively attributed to the rather low number of states accessible to the H + 3 complex at the temperature regime (11 K-33 K) considered there. In order to elucidate the issue more QM calculations on sufficiently precise PESs are required.…”

Ortho–para-H2conversion processes in astrophysical media

“…SQM [66,67] calculations were also performed for the H + + H 2 reaction and its isotopic variants [17][18][19]84,85]. A recent experimental study [86] has shown that the observed resonances here can be directly related with H + -H 2 radiative association processes. A comparison between the SQM and the TIQM results could confirm or not the statistical behaviour of H + + H 2 .…”

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

“…He, will cause in-trap collisions that will couple translational degrees of freedom to the internal states of the molecular partners through the spatial anisotropy of the interaction's potential energy surfaces (PES) between the partners in the trap. Such a picture also requires defining a "cold" He partner, a feature of the present processes that we shall further discuss later on: its translational temperature will be assumed to be experimentally settable in the range between 4 K and 300 K and will therefore be treated as an adjustable parameter during the calculations [7][8][9]. The collisional energy transfer will therefore provide an important path to finally produce thermally cold partners which are also in the ground-states of all the molecular ion's forms of internal energy (electronic, vibrational, and rotational), with the exclusion in the present study Contribution to the Topical Issue "Dynamics of Molecular Systems (MOLEC 2016)", edited by Alberto Garcia-Vela, Luis Banares and Maria Luisa Senent.…”