Program POTCURV is written in FORTRAN IV extended and run on a CDC Cyber 170-750with 30000 (octal) words of 60 bits. I t contains103 statements. Plots are drawn by a CALCOMP digital plotter, by calls to original FORTRANoriented software. The transportability of the program to another graphics system can he made easily owing to an extensive description of the calling sequences of the plotting routines given in the documentation. Listing, description of the program, and sample executions can be obtained, free of charge, by writing to Dr. J. Lievin. The author is grateful to Dr. J. Olhregts and Mr. J. Breulet for critical reading of the manuscript.
Microcomputer-Simulated Liquid Chromatography James E. DlNunzlo Wright State University Dayton, OH 45435
and X'&+ Figure 6. Potential curves of the .HIovt
states of I?. (Lievin)
Another option to he activated is the plot of an harmonic potential curve of the form with the force constant k related to the vihrational frequency by the expression (17) The following data are t o be entered interactively: the number of states, n, the energy scale, and for each state the values of T., D., Re, /3, k , n,, we and wax.. An example of plot is given in Figure 6 where the potential curves of the B3n,,+ and X'Z: states of the I2 molecule are drawn. We suggest that students discuss the following relevant features appearing on such a graph: 1) The differences hetween the vibrational frequencies, anhar-
monieities, and dissociation energies of the two electronic . + . t n .
2, The relative positions of the powntial minima. 3) The region of validit). of the hdrrnunicosrillstorapproximation. 4, The different aturnic orudurts dissorintiun limlr (dircusr the
Wigner-Witmer rules).'
5) The displacements of the turning points of the vibrational levels between the two states (discussthe Franck-Condon principle).The students can also draw different Morse potential curves for the
same electronic state by calculating the dissociation energy in several ways: 1)Birge-Spooner extrapolation (eqn. (3)),2) using (18) the Morse-Pekeri expression for the a. constant, 3) using hands convergence (observed in same eases (12),electronic term and atomic excitation energy. Using one of the two last ways to determine D. will provide potential curves with a more correct shape a t long-range distances. However, it is important to note that a parallel correction of the vibrational constants we and w,x, is not possible and that the values of these constants obtained from a Birge-Spooner graph are only valid for small values of the vibrational auantum number. Therefore.. the oromam . " will use as independent data the values of D. and we, o,x, to plot modified Morse ootential curves toeether with fust vibrational energy levels. 778
Journal of Chemical Education
Liquid chromatography is a powerful technique, useful in many areas of chemistry. If this technique is used, a large number of parameters can be varied in order to achieve adesired goal, i.e., separation of a group of solutes. Because of time limitations in the normal laboratory schedule, it is impossible for students to obtain actual exoerience in all asoects of liauid chromatography. In many cases, students obtain only avague idea of its power. The purpose of the computer program described here is to allow students to observe the full potential of liquid chromatography within the time limits of a normal laboratory period. The program is designed to be used in a iunior-senior analvtical instrumentation course. In order tooperare the program, the student is required to obtain from the literaturean articledealing with the separation of components hy liquid-liquid partition chromatography. This article must meet the t'ollou,ina requirements. The article must deal with the separation of a t least three solutes. The separation should be performed by reverse phase liquid chromatography (preferably methanol and water as mobile phase solvents). Data must be available for the separation of the solutes using a t least two mobile phases containing different proportions of the same solvents. This data can be given in terms of tabulated values of capacity factors a t various mobile phase compositions or actual chromatograms from which the capacity factors can be measured. When the program is initiated, the student is asked to enter the caoacitv nercent volume of or. .factor and corresoondine". ganic solvent in the mobile phase for each solute at each of two different mohile phase compositions. All the data for each solute is entered in turn. After the student enters the data for each solute, the computer will calculate and display the capacity factors for that solute over the mobile phase composition of 0-100% organic solvent in 5% steps. After all the data have been entered, the student is asked to oerform several exoeriments. First, using a set of standard ch;omatographic codditions written into t h e programs the student examines the influence of the mobile phase composition on the separation of the chosen solutes. This is done by selecting several mobile phase compositions by entering the selected percent organic solvent and obtaining the chromatographic data. In a similar manner, the student examines the influence of the stationary phase particle size, column length, and mobile phase flow rate on the separation. These parameters are examined using an optimum mobile phase composition selected from the results obtained in the first experiment. The total time reauired to run the . oromam is about three hours. The chromatoeraohic data from each exoeriment are displayed hy the micr&omputer in two ways: First, after each oarameter is entered. the chromatoeram is dis~laved eranh. . . ically. This is a usefu
