Comparing Spectra for Isotopologues

GaussView makes it easy to compare spectra for different isotopologues of the same structure. To do so, you first define the desired isotopes for each isotopologue using the Atom List Editor. Then you generate vibrational data sets for each one (see below). Once completed, you can use the Display Vibrations dialog to examine the spectra and normal modes.

r_vib_isotope.tif
Comparing Normal Modes for Three Isotopologues

In the Atom List Editor (top), we have defined three isotopologues for this simple molecule: one with the standard isotopes, one with deuterium replacing each hydrogen, and a third with tritium replacing a single hydrogen. The normal mode corresponding to the sixth frequency shifts location for each isotopologue (compare the values beneath each View window). The motion for the first two isotopologues is similar, but the mode for the tritium form has the motion confined to that atom.

The buttons in the upper right can be used to define isotopologues and generate frequency data for them.

Defining Additional Isotopologues

Go to the Atom List Editor, and click the arrow on the ā€œIā€Ā icon. Add the next isotopologue to the column.

Adjust the isotope values as appropriate.

Generating and Displaying Frequency Data for an Isotopologue

Click New Data in the Vibrations window. The window shown below appears, allowing you to choose the desired isotopologue:

Back in the Vibrations windows, use the Active Data popup to pick a data set (isotopologue) to display:

The currently displayed set is indicated by a label to the right of the popup. The spectrum, normal mode animation and other displays will reflect the selected isotope set.