Ab InitioCalculated Rotation–Vibration Line Strengths for the (vHH= 0 → 1 ) Transition of HeH+2

High-Resolution Spectroscopy of Cluster Ions

“…The intermolecular bend and stretch frequencies are predicted to be 646 and 716 cm -1 , respectively . The excited H−H stretching state lies at approximately 1830 cm -1 , slightly above the H 2 + + He dissociation limit ( D 0 = 1754 cm -1 ), and is predicted to be substantially broadened by predissociation. , …”

“…Several H 2 + −He PESs have been developed and used to determine bound-state levels and effective rotational constants. ,− The most recent of these was carefully constructed in an attempt to explain the near dissociation MW transitions . It is fitted to ab initio points in the short to intermediate range and has the long-range form expected from induction, electrostatic, and dispersion interactions between the constituents.…”

Numerical techniques for the evaluation of non-adiabatic interactions and the generation of quasi-diabatic potential energy surfaces using configuration interaction methods

“…Compared with previous calculations [66,67,71,72] the agreement for the spectroscopic parameters and the lowest vibrational levels is within a few wavenumbers, but the di erence increases to 30 cm ¡1 for the lowest overtone of HeH ‡ HeD ‡ 2 . The diagonal non-adiabatic corrections have been estimated as 1 cm ¡1 for the lowest vibrational frequencies and approximately 3 cm ¡1 for the highest bound vibrational levels.…”

“…Compared with Tennyson et al [71], we treat the complex not as weakly interacting He ¢ ¢ ¢ H ‡ 2 but as a bound HeH ‡ 2 system with the He atom localized at one molecular end, neglecting entirely the tunnelling between the two equivalent minima and the splittings between para-H ‡ 2 ( j-even in table 2) and ortho-H ‡ 2 ( j-odd) [71] states which, for the low lying levels, have been found negligible in all previous treatments. The main advantage of this approximation is that it requires only local representations of the PES avoiding global representations [66,67,71,72], and improving the accuracy of the PES close to the minima. To this purpose the Jacobi coordinates used for the energy calculations have been converted to the corresponding valence coordinates, the bond stretchings r…HH †, R…HHe † and the angle bending …HHHe †, to represent the PES and the non-adiabatic corrections by the polynomial expansions …r;R; †ˆX…”

Rovibrational Energies of Triatomic Molecules by Means of the Rayleigh–Schrödinger Perturbation Theory

“…The quality of previous bound state calculations (13) of HeH 2 ϩ has suffered from the insufficient accuracy of the available global potential function (14 -15). Therefore, most recently the lower part of the potential surface up to the first dissociation channel (He ϩ H 2 ϩ ) was recalculated at a high-accuracy level of ab initio theory (16) and all bound rotation-vibration energies and the lowest quasibound levels were determined variationally (17)(18). In HeH 2 ϩ , the rather shallow potential below the first dissociation limit holds only a few bound low-frequency vibrational levels and the first excited level of the high-frequency H-H stretching motion is already above the dissociation threshold.…”