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Manuscript Title: Computer assistance in the analysis of molecular spectra. I. Rotational structure of high resolution singlet-singlet bands.
Authors: F.W. Birss, D.A. Ramsay
Program title: ASYROT
Catalogue identifier: ACDS_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 38(1985)83
Programming language: Fortran.
Computer: AMDAHL 580/5840.
Operating system: MTS.
RAM: 55K words
Word size: 32
Peripherals: disc.
Keywords: Asymmetric rotor, Molecular constants, Molecular physics, Spectra, Rotational analysis, Rotational Band structure, Rotational hamiltonian.
Classification: 16.2.

Other versions:
Cat Id Title Reference
ABBA_v1_0 ASYROT PC CPC 47(1987)361
ACPS_v1_0 Frasyrot CPC 79(1994)555

Nature of problem:
The rotational structures of vibrational and vibronic bands of asymmetric rotor molecules often exhibit in excess of 1000 assigned frequencies. The determination of the parameters of the model Hamiltonian by a least-squares fit of calculated to observed frequencies requires the aid of computer calculations.

Solution method:
The preparation of the calculated frequencies and corresponding intensities follows standard methods adapted to the phase conventions of Condon and Shortley. The derivatives required for the least-squares procedure are calculated by the Hellmann-Feynman theorem. The derivatives are also used for approximate recalculation of the transition frequencies upon modification of the values of the parameters. Given a reasonably precise set of parameters from a partial analysis of a band, the automatic assignment feature can, with extreme care, be used for rapid proposal of assignments.

Restrictions:
The rotational quantum numbers J and Ka are restricted to maximum values of 100 and 50 respectively. Provision is made for 5000 calculated frequencies, each of which may have a corresponding assigned observed frequency. The numbers of assigned and unassigned observed frequencies which may be input at any one time is 1500 and 2500.

Running time:
For a representative band with a maximum J of 30 and a maximum Ka of 12 with 2700 calculated frequencies, 1200 assigned observed frequencies and 900 unassigned observed frequencies, the running times were 3.4, 1.6, 4.7, 1.5, 3.0, 2.7 and 1.3 seconds for phase I to VII respectively. The compilation time of the program was 6.3 seconds.