States near dissociation in H⁺₃

• Main Author: Munro, James Julian
• Published: University College London (University of London) 2006
• Subjects: 523.015012
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.440471

Ah initio calculations contributing to an understanding of the infra-red near-dissociation spectrum of H⁺₃ are performed. All the bound vibrational nuclear-motion states and all the J=3 ro-vibrational states of H⁺₃ are calculated using a discrete variable representation (DVR) of the Hamiltonian on a massively parallel computer. The vibrational motion is evaluated in Jacobi and Radau coordinates. The rotational motion is evaluated using a z-perpendicular embedding of body-fixed co-ordinates. The vibrational band origins and ro-vibrational J=3 energy levels are calculated using an optimised basis set of effective size 696,960 x 4(J + 1). This results in ro-vibrational states which are converged to an unprecedented level of accuracy. Preliminary resonance state calculations of a similar accuracy are also performed by extending the bound state calculations using a complex absorbing potential method. The calculations performed are very large and therefore the algorithm has been extensively parallelised on a supercomputer. Several aspects of the DVR based algorithm are improved at every level of the calculation. An accurate and efficient system for performing resonance calculations based upon complex absorbing potentials is developed with an accuracy primarily dependant upon basis set completeness. The calculated vibrational nuclear-motion states are examined near dissociation using a number of methods. A number of long range van der Waals-like states are found to exist near dissociation. These asymptotic vibrational states are studied, graphically, through classical motion calculations and expectation values of the wave functions. Large basis 3D wave functions are also produced which are suitable for dipole transition calculations and could soon lead to a better understanding of the infra-red near-dissociation spectrum of H⁺₃.