Gilbert F. Pollnow and Anton J. Hopfinger' Wisconsin State University Oshkosh, 54901
A Computer Experiment in Microwave Spectroscopy
The ever-increasing emphasis on mathematical and quantum mechanical sophistication in the undergraduate chemistry curriculum has also resulted in the inclusion of computer and microwave spectroscopic techniques (1, g). Experiments suitable for student use however, have been limited to those molecules whose spectrum could be expressed in closed form in terms of the rotational parameters of the molecule. Unfortunately, most molecules are not spherical or symmetric top types, and hence, cannot be used for this purpose because of the time-consuming nature of the energy level calculations. I t is the purpose of this paper to describe the application of a computer program (3) which reduces the time to calculate the rigid rotor energy levels for any molecule t,o a mnt,ter of minutes, or an hour or two depending on t,hemaximum value of the angular inomentum quantum number (J > 15). This progrbm has been derived for a course in the application of the digital computer to chemical problems which is offeredby one of the aut,hors in the chemistry department to seniors and graduate students. Since the backgrounds of the students taking this course are quit,e varied, relatively few have the necessary quantum mechanical experience to carry out a complet,e spectral analysis in a reasonable time successfully. Hence, use of the experiment at this university has been reserved as a special problem for those students with an unusually good background in chemistry and physics, e.g., a double major. Program The program is written in Fort,ran I for the basic IBM 1620 with 20 X storage and automatic divide hardware. Input aud output are via the standard IBM 1622 Card Read/Punch; however, switch options are utilized to provide t,ypewriter ont,put when desired. Sequent,ial instructions are automatically provided by the typewriter as processing takes place. If the output is punched on cards they may he listed on the IBM 407 or by the computer itself with an appropriate program. The program computes the principle moments of inertia, center of mass, energy levels, and corresponding frequencies of any rigid asymmetric rotor consisting of 50 or fewer particles for values of the angular momentum quant,um riumber, J < 1.5. Calculation and classification of the energy levels follows the procedure described by Icing, Hainer, and Cross (4) for their 111' representation which identifies the a,b,c principle axes in the rotor with the space fixed x,y,z axes, respectively, so that
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