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Abstract

On the basis of both experiment and theory, accurate rotational–vibrational line positions and energy levels, with associated critically reviewed labels and uncertainties, are reported for the ground electronic state of the H3+ molecular ion. An improved MARVEL algorithm is used to determine the validated experimental levels and their self-consistent uncertainties from a set of 1610 measured transitions and associated uncertainties, coming from 26 sources. 1410 transitions have been validated for ortho-H3+ and para-H3+, 78 belong to floating components of the spectroscopic network (SN) investigated and thus left unvalidated, while 122 measured transitions had to be excluded from the MARVEL analysis for one reason or another. The spectral range covered by the experiments is 7–16 506 cm–1 . Altogether 13 vibrational band origins are reported, the highest J value, where J stands for the rotational quantum number, for which energy levels are validated is 12. The MARVEL energy levels are checked against ones determined from accurate variational nuclear motion computations employing the best available adiabatic ab initio potential energy surface and exact kinetic energy operators. The number of validated and thus recommended experimental-quality rovibrational energy levels is 652, of which 259 belong to ortho-H3+ and 393 to para-H3+. There are 105 further energy levels within floating components of the SN. The variational computations have been performed both without and with a simple nonadiabatic correction, whereby nonadiabaticity is modeled by the use of a non-nuclear vibrational mass. The lists of validated lines and levels for H3+ are deposited in the Supporting Information to this paper.