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Highly excited ro-vibrational states of small molecules using discrete variable representations

Henderson, James R; (1990) Highly excited ro-vibrational states of small molecules using discrete variable representations. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Calculated ro-vibrational levels (J ≤ 4) and transition intensities are presented for 7Li+3 and 7Li2 6Li+. These studies are made using conventional Finite Basis Representation (FBR) methods. A formulation of the nuclear motion problem for small molecules is then presented in the Discrete Variable Representation (DVR). The theory is developed in a highly generalised set of internal co-ordinates using an exact Hamiltonian operator. Having used the DVR for vibrational (J = 0) calculations, it is rather simply extended to ro-vibrational (J > 0) case. It is demonstrated that the DVR is extremely powerful in dealing with molecules that can undergo very large amplitude (coupled) motions on what may be a particularly complicated potential energy surface. Calculations on the isomerising LiCN/LiNC system are presented using a 2D (CN frozen) potential energy surface. Some 900 vibrational levels are stabilised using a DVR in the angular co-ordinate of scattering (or Jacobi) co-ordinates. Contour plots of the wavefunctions are made and analysed; this yields information about the very highly excited dynamics of the system, well above the isomerisation barrier, for the very first time. Full three-mode calculations on the H+3 molecular ion are presented, using a very accurate ab initio potential energy surface. Ro-vibrational studies are made using a DVR in the angular co-ordinate of scattering co-ordinates. A multidimensional DVR in scattering co-ordinates is then employed and three H+3 surfaces are used. These calculations converge all the J = 0 bound states of the system to within 10cm-1, giving at least 881 states for each potential. The wavefunctions are analysed in an attempt to find assignablel or spatially localised states. The significance of these calculations to the unassigned near-dissociation spectra is discussed.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Highly excited ro-vibrational states of small molecules using discrete variable representations
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Pure sciences; Lithium
URI: https://discovery.ucl.ac.uk/id/eprint/10120809
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