H ₃ ⁺ near dissociation: theoretical progress

Abstract

The observation of an infrared spectrum of the H + 3 molecular ion at its dissociation limit by Carrington and co-workers has presented a tremendous challenge to theory. To compute this spectrum it is necessary to model accurately the global potential energy surface of H + 3 , vibrationally excited states at dissociation, rotational excitation, lifetimes of rotationally excited`shape' resonances, and infrared transition dipoles near dissociation. Progress in each of these aspects is reviewed and results are presented for highly excited vibrational levels using a new ab initio global potential. The use of massively parallel computers in solving aspects of the problem is discussed.

Rotation-vibration states of H3+ at dissociation

“…Convergence was established both by self-consistency checks and by comparison with calculations performed in Jacobi coordinates. 34 The calculations presented here were based on the use of N 3 ϭ9984 which is sufficient to converge the energy levels to within about 1 cm Ϫ1 . We were able to perform larger calculations than this for Jϭ0, 34 but the JϾ0 calculations require more local memory.…”

“…34 The calculations presented here were based on the use of N 3 ϭ9984 which is sufficient to converge the energy levels to within about 1 cm Ϫ1 . We were able to perform larger calculations than this for Jϭ0, 34 but the JϾ0 calculations require more local memory. This is due to the need to save wave functions in memory which are used to compute the matrix elements off-diagonal in k. This constraint meant that N 3 ϭ9984 was the largest JϾ0 problem that could be attempted with the present facility.…”

Perspective: Accurate ro-vibrational calculations on small molecules

“…Attempts to model these spectra quantum-mechanically have so far given little insight into the underlying physical processes involved and certainly provide nothing approaching any line assignments. [87][88][89] Before moving to larger systems, it is worth mentioning the intriguing H + 5 system. This four-electron ion does not provide a benchmark for accuracy but instead provides a fundamental fluxional system in which the atoms freely interchange even at energies easily probed by spectroscopy.…”

Chemical probing spectroscopy of H3+ above the barrier to linearity

“…With the dissociation energy of H + 3 being more than 35 000 cm −1 [15] these experiments apparently probed an energy region very close to the dissociation limit. The origin of these lines as well as the underlying coarse structures are still unresolved [11].…”

“…The highenergy region is challenging theory in particular since the basis sets optimized for triangular geometries near equilibrium are ill-suited to treat linear geometries [11]. In an effort to create a surface that maintains high accuracy in the equilibrium region and includes the correct long-range behaviour at higher energies, Tennyson and coworkers employed a potentialswitching approach in order to use the best-available calculations in each respective energy region [8,12].…”