An approach for multi-color action spectroscopy of highly excited states of H3+

The H3+ ion is the simplest polyatomic molecule. Apart from its fundamental role as a benchmark system for theoretical calculations, it has attracted a lot of attention as one of the main drivers of an active interstellar ion-neutral chemistry network. H3+ spectroscopy has contributed greatly to astrochemistry, and experiment and theory have both developed tremendously throughout the years, following the ground-breaking work by Oka. To date, the highest-lying identified H3+ transitions were obtained using an action spectroscopy technique, employing stored H3+ ions in a cryogenic ion trap. This approach was pioneered by Schlemmer and Gerlich for N2+ , and is widely used today – in one form or another – for spectroscopic studies of interstellar ions. In this work, we explore the possibility to extend the range for H3+ action spectroscopy even further, into the regime above 20000cm-1, in order to bridge the gap to the rich pre-dissociation spectrum of states near the dissociation limit that was obtained by Carrington et al. and remains unassigned after more than 30 years.