Home Page What's New List of our Products Sales List of Seminars/Workshops Corporate Partners Customer Support










Isotope Effects on Molecular Vibrations

This example should work well for physical chemistry in the discussion of molecular vibrations. Optimize the structure of HCl at the HF/3-21G(*) level and calculate the vibrational frequency. Translational modes are eliminated so you should see a single vibration at 3151 cm-1. This number is 5.4% above the experimental value of 2989 cm-1. Which atom moves when you animate the vibration?

What happens to the vibrational frequency when hydrogen is changed to deuterium or tritium? Each version of the program provides a way to make this change. For example, in Spartan PC Pro, this feature is provided in the Display-Properties menu when you click on an atom. Create a new model for D-Cl in which the H has been changed to D and submit this for optimization and frequency calculation. Create a third model for T-Cl and submit this. Each job should give the same electronic energy and geometry but different vibrational frequencies.

HOD makes another excellent example. Change one hydrogen in water to a deuterium and then submit the job for optimization and frequency analysis at the HF/3-21G level. The C-H and C-D vibrational modes now have quite different frequencies!


Copyright © 1995-2001 Wavefunction, Inc.
All Rights Reserved.

Home
News
Software
Books
Workshops/Seminars
Sales
Corporate
Support
Questions, comments, suggestions about this site? webmaster@wavefun.com