An Interactive Computer Program for Microwave Spectroscopy Structural and dipole moment determinations, isomerization and intramolecular conversion studies, confarmational analyses, and molecular magnetic properties of gaseous molecules are frequent topics for microwave experiments of many chemistry undergraduates and graduate students. The assignment of a microwave spectrum, i.e., the quantum number labeling of the states involved in each transition, is still tedious and time-consuming when compared with the duration of the experiment itself. In order to better facilitate the computation and localization of the energy levels, we have written a new and more versatile Fortran IV program applicable to a variety of microwave experiments cited in this Our pragram has the following features. (1) The student can generate the energy levels for any arbitrary values of the asymmetry parameter, Kappa, with a remote terminal typewriter input. We have used TSO (Time Sharing Option) as the software support far the IBM 2741 typewriter terminals or model 33 and 35 teletypes connected to an IBM 360165 and IBM 3701145. This allows a high degree of interaction between the student and computer. Alternatively, we have also performed RJE (Remote Jab Entry) through CPS (Conversational Programming System) on an IBM 360165. (2) Complementing the above concept of remote jab entry, we have applied the mast stable, reliable, and efficient numerical algorithm3 to find the roots of the four secular equation^.^ For rotational quantum number J = 40 (i.e., for a quasi-symmetric submatrix of order approximately 512) for any arbitrary value of Kappa, approximately 0.18 sec of CPU time is required for the diagonalization procedure (based on an IBM 360165). (3) Although the program is designed to be optimal far both IBM 360 series (real memory) and IBM 370 series (virtual memory) a student can also execute the program in card form in any modern third generation digital computer (e.g., UNIVAC 1108, CDC 6600/7600, RCA Spectra 70, etc.) with only minor modifications. (4) The accuracy of a t least 14 significant figures is made possible by using douhle-piecision arithmetic, and the program is extensively overlaid to economize on core storage. (5) There are two options for the input, namely, the values of Kappa and J , or the input of the atomic masses and the Cartesian coordinates of the molecule together with J. The output consists of the energy levels in tabular form labeled according to the method of King, Hainer, and Cross,' with or without an approximate centrifugal distortion correction. The results of this program agree with the published tables far J 5 40 of Allen and C ~ o s s and , ~ in addition yield results of similar accuracy for J 5 100. However, in practice the maximum value of J permitted by remote entry will depend on the size of the partition allocated for this purpose, and the relatively slow output rate of the 2741 communications terminal. Complete documentation, program listings, and sample input/output are available from G.F.P. upon request.
'Pollnow, G. F., and Hopfinger, A. J., J. CHEM. EDUC., 45,528 (1968).
Schwendeman, R. H., Volltrauer, H. N., Laurie, V. W., and Thomas, E. C., J. CHEM. EDUC., 47,526 (1970). Chung, C. S. C., to be published. King, G. W., Hainer, R. M., and Cross, P. C., J. Chem Phys., 11,27 (1943). 5Allen, H. C., Jr., and Cross, P. C., "Molecular Vih-Rotors," John Wiley & Sons, Ine., New York, 1963. (For listing of tables J 5 40). Gilbert F. Pollnow C. S.C. Chung University of Wisconsin-Oshkosh Oshkosh, 54901
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