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Manuscript Title: Particles-on-a-sphere method for computing the rotational-vibrational spectrum of H2O.
Authors: D.M. Leitner, G.A. Natanson, R.S. Berry, P. Villarreal, G. Delgado-Barrio
Program title: OS2D
Catalogue identifier: ABDV_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 51(1988)207
Programming language: Fortran.
Computer: CRAY XMP-48.
Operating system: CTSS.
RAM: 22K words
Keywords: Molecular, Vibration.
Classification: 16.3.

Nature of problem:
The energy levels of the overall rotations coupled with bending vibrations are computed by solving the Schrodinger equation for two particles on a sphere. The effective radial distance of the hydrogen atoms from the oxygen atom and the effective mass of the oxygen atom calculated in SP2D are used as the radius of the sphere and the mass of the particle at the center of the sphere, respectively. Rotational- bending levels are calculated for each angular momentum quantum number.

Solution method:
The bending potential calculated in SP2D is expanded in terms of Lengendre polynomials. For OS2D, only the bending potential calculated using the wavefunctions at the equilibrium bending angle can be input. The basis functions used to solve the particles-on-a-sphere equation are coupled spherical harmonics. Bending levels for all rotational quantum numbers of interest are calculated variationally.

Running time:
For the calculation of bending states with no rotation for the first 3 stretching levels, a run using 40 coupled spherical harmonic basis functions takes about 9 cpu seconds on the Cray. If then the first 2 rotational levels are calculated for all 3 levels of the stretching modes, the program runs for about 90 cpu seconds.