Spectroscopy and dissociative recombination of the lowest rotational states of H3+

TL;DR

This study investigates the dissociative recombination of the lowest rotational states of H3+ ions using advanced cryogenic and spectroscopic techniques, revealing insights into their rate coefficients, dynamics, and fragmentation geometries.

Contribution

It provides new experimental data on the recombination rates and dissociation dynamics of cold H3+ ions in specific rotational states, using a combination of storage ring and laser spectroscopy methods.

Findings

Para-H2 increases para-H3+ contribution by ~20%.

H3+ rate coefficients are similar for normal- and para-H2 sources.

Fragmentation geometries show broad shapes with slight symmetry enhancement.

Abstract

The dissociative recombination of the lowest rotational states of H3+ has been investigated at the storage ring TSR using a cryogenic 22-pole radiofrequency ion trap as injector. The H3+ was cooled with buffer gas at ~15 K to the lowest rotational levels, (J,G)=(1,0) and (1,1), which belong to the ortho and para proton-spin symmetry, respectively. The rate coefficients and dissociation dynamics of H3+(J,G) populations produced with normal- and para-H2 were measured and compared to the rate and dynamics of a hot H3+ beam from a Penning source. The production of cold H3+ rotational populations was separately studied by rovibrational laser spectroscopy using chemical probing with argon around 55 K. First results indicate a ~20% relative increase of the para contribution when using para-H2 as parent gas. The H3+ rate coefficient observed for the para-H2 source gas, however, is quite similar to the H3+ rate for the normal-H2 source gas. The recombination dynamics confirm that for both source gases, only small populations of rotationally excited levels are present. The distribution of 3-body fragmentation geometries displays a broad part of various triangular shapes with an enhancement of ~12% for events with symmetric near-linear configurations. No large dependences on internal state or collision energy are found.