Spectroscopy of H ₃ ⁺ based on a new high-accuracy global potential energy surface

Abstract

The molecular ion H + 3 is the simplest polyatomic and poly-electronic molecular system, and its spectrum constitutes an important benchmark for which precise answers can be obtained ab initio from the equations of quantum mechanics. Significant progress in the computation of the ro-vibrational spectrum of H + 3 is discussed. A new, global potential energy surface (PES) based on ab initio points computed with an average accuracy of 0.01 cm −1 relative to the non-relativistic limit has recently been constructed. An analytical representation of these points is provided, exhibiting a standard deviation of 0.097 cm −1 . Problems with earlier fits are discussed. The new PES is used for the computation of transition frequencies. Recently measured lines at visible wavelengths combined with previously determined infrared ro-vibrational data show that an accuracy of the order of 0.1 cm −1 is achieved by these computations. In order to achieve this degree of accuracy, relativistic, adiabatic and non-adiabatic effects must be properly accounted for. The accuracy of these calculations facilitates the reassignment of some measured lines, further reducing the standard deviation between experiment and theory.

Ab initio computational spectroscopy and vibrational dynamics of polyatomic molecules: Applications to syn and anti-CH3CHOO and NO3

“…There has been substantial progress by a number of groups in achieving this goal for triatomic molecules, with a number of codes able to do such calculations, for a sample of such codes see Refs. [1][2][3][4]. Thus, it is fair to state that rigorous, ab initio line-list computational spectroscopy for triatomics is essentially ''solved''.…”

“…There has also been substantial progress in achieving this goal for general tetraatomics, see for example Refs. [5][6][7][8] and for some larger, albeit semi-rigid molecules, such as CH 4 [9,10], C 2 H 4 [11,12] and CH 3 OO [13]. There has also been significant progress in developing global, i.e., describing multiple minima and in some cases fragment channels, PESs for tetraatomics, based on strict mathematical fitting of tens of thousands of high-level electronic energies.…”

Quantum astrochemical spectroscopy

“…The rotational constants of ArH 1 3 match experiment to within 60 MHz, and the Ar 2 H 1 3 CcCR QFF m 1 breathing mode of 3274.6 cm 21 is within 16 cm 21 of expeirment done in the same study. However, the ArAH force constants of 0.478761 mdyne/Å 2 and 0.331600 mdyne/Å 2 , respective of ArH 1 3 and Ar 2 H 1 3 , indicate that these structures are likely not present in observable quantities in the ISM since they easily break down into argon atoms and the astrochemically important [117,118] …”

Low-Temperature Scattering with the R-Matrix Method: The Morse Potential

“…For heavy particle scattering this procedure is particularly appropriate for reactive or non-reactive collisions which occur over deep potential energy wells. Thus, for example, H + H 2 collisions do not occur over a deep well as the H 3 system is only weakly bound [7], while collisions between H + + H 2 occur over the deep well of the H + 3 potential energy surface [8].…”