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Manuscript Title: Computer assisted analysis of singlet-triplet rotational spectra: application to case (A), case (B) and case (AB) coupling cases in polyatomic molecules.
Authors: R.H. Judge, E.D. Womeldorf, R.A. Morris, D.E. Shimp, D.J. Clouthier, D.L. Joo, D.C. Moule
Program title: STROTAB
Catalogue identifier: ADCA_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 93(1996)241
Programming language: C.
Computer: HP Apollo 710.
Operating system: HPUX 9.05, MSDOS 6.0.
RAM: 350K words
Word size: 16
Keywords: Asymmetric rotor, Centrifugal distortion, Case (a), Case (b), Case (ab), Least squares analysis, Molecular constants, Singlet-triplet Rotational Band structure, Spin centrifugal Distortion, Spin constants, Spectra.
Classification: 16.2.

Nature of problem:
The rotational analysis of the singlet-triplet electronic spectra of orthorhombic polyatomic molecules has hitherto been restricted to molecules which follow case (B) coupling [1,2]. A more general program is required to analyze spectra of molecules which exhibit case (A), case (AB) or case (B) coupling in the triplet state.

Solution method:
The hamiltonian developed by DiLauro [3] for use in the case (A) limit is extended to include the effects of centrifugal distortion and spin centrifugal distortion. The matrix elements have been evaluated and appear in a companion paper to this article [4]. The method of Creutzberg and Hougen [6] is followed in reducing the size of the matrices that require diagonalization. The intensity tables of Creutzberg and Hougen [6] are also used in the calculation of the transition intensities. The program allows for the mixture of quantum labels used to assign the transitions under the case (A) and case (B) coupling schemes.

Restrictions:
The rotational quantum number restrictions are J <= 255 and K (or P) <= 127. The allowed transition frequency less the band origin frequency must be in the range of +-10000 cm-1. Up to five decimal places may be reported. The number of observed lines is limited by the dynamic memory and the amount of disk space available. Only molecules of symmetry D2h, D2 and C2v can be accommodated in this version. Only the constants of the excited triplet state may be varied.

Running time:
For the test data supplied (case (B) thioformaldehyde, J=31, Ka=8, with 588 assigned observed transitions), 14 constants varied, and two least squares cycles, the running time was 4 minutes under the HPUX operating system. The MSDOS version running time was 15 minutes.

References:
[1] F.W. Birss, "STROT", Unpublished singlet-triplet least squares rotational analysis FORTRAN program.
[2] T.J. Sears, Comp. Phys. Reports 2(1984)1. T.J. Sears, Comp. Phys. Comm. 34(1984)123.
[3] C. DiLauro, J. Molec. Spectrosc. 35(1970)461.
[4] R.H. Judge, A.A. Korale, J.J. York, D.L. Joo, D.J. Clouthier and D.C. Moule, submitted to J. Chem. Phys.
[5] F. Creutzberg and J.T. Hougen, Can. J. Phys. 45(1967)1363.
[6] F. Creutzberg and J.T. Hougen, J. Molec. Spectrosc. 38(1971)257.