interpretative Frank DeHaan Occidental College Lor Angeler, California
An IR Simulator for the Undergraduate Physical Chemistry Course K. D. Summerhays, T. A. Gruhn, and J. P. McCarthy University of San Francisco Sun Francisco, California 94117 The recording and analysis of rotation-vibration spectra of simple molecules in the gas phase is a well-established experiment in the undergraduate physical chemistry laboratory. The subject encompasses a good deal of basic quantum mechanics (e.g., the harmonic oscillator and rigid rotor with their refinements and spectral selection N ~ S )and illustrates the Boltzmann distribution and isotope effects. To many students, the experiment serves as an introduction to high resolution instrumentation and to a technique which yields molecular parameters to a high degree of accuracy. We have developed ( I ) a Fortran IV program, IRSIM, which we feel enhances the presentation of this topic, and, in addition, makes the experiment available on a "Dry Lab" basis for those institutions lacking high resolution. infrared spectrometers or for those whose instruments tend to malfunction on occasion. The program produces, via a Cal-Comp plotter, the fundamental rotation-vihration hand of diatomic molecules at any temperature. The output was designed with the aim of obtaining realisticlooking spectra (the performance of our Perkin-Elmer Model 421 spectrophotometer being used as a guide). The spectral lines are given a Lorentziau shape with a halfwidth of 0.5 cm-1 and are displayed on a 20 X 70 cm chart with an adjustable scale whose normal value is 1 cm-l/mm. The frequencies of the lines with respect to a plotted reference mark can be read conveniently and with precision by using an overlay of transparent graph paper. Required input consists of the atomic masses, percentage of each isotope, force constant, interatomic distance, the anharmonicity and rotation-vibration interaction con-
experiments stants, and the temperature. We have compiled a table based on Henherg (2) which gives information for many diatomics and will make it available with the program listing. Optional input includes ~ a r a m e t e r saltering the standard scale and resolution. T h i printer output inciudcs for each isotopic comhination, the freauencies and re1atk.e intensities of the spectral lines plus acomplete tabulation of all the parameters arising from the usual methods (3, 4) for reduction of the spectral data. Computer programs for performing these calculations have appeared in this Journal (5, 6). As an extra feature, the exact rotational partition function is compared to the classical approximation. This has merit in view of the wide range of temperatures and moments of inertia one may deal with. In the hands of the instructor, IRSIM can he used to generate multiple spectra as problem sets or as a source of material to supplement lectures. Students can "experiment" with the proaram and discover the effect on the shape of a specti& of factors such as the temperature, the rotation-vihration interaction constant, or instrument resolution. The program listing contains a generous quantity of comment statements and the simplified instructions provided include a sample data deck. On our UNNAC 70/46, execution times are generally less than 10 s per spectrum. Core requirements are approximately 23K bytes. Inquires and requests for listings should be addressed to KDS. We will provide a copy of an HC1 spectrum to those institutions lacking access to a Cal-Comp Plotter. Literature Cited 11) Reference to an earlier venion of this pmgrsm was given by Peteraon, D . L.. and Puller, M . E . , J.CHEM.EDUC.,48.314 (1971) 12) Henbelg, G., "Spectra of Diatomic Moleculen." 2nd ed., D . Van Nosfrand Co.,
1s Shamaker, 0. P.. bsrland. C. W.. and Steinfeld. J. I.. "Erpoximent~in Physical
Chemistry," M a d . . MeGraw-HillBook Co.,NowYork, 1914, pp15U-9. 14) Daniels. F.. Williams, J. W., Bender, P., Albeny, R. A , Cornluell, C. W., and Harriman. J . E., "Experimental Physical Chernisw." 7th ed.. MeGraw-Hill Book Co.. NauYork, 1910. pp 241-56. ( 5 ) Richarda,L. W., J.CHEM.EDUC.. 43,552(1966) 16) Bader.M., J.CHEM. EOUC.,46.M6l1969).
Volume 52, Number 3. March 1975
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