A B C Rotational Constant Calculator
calculates the point group, Principal Moments of Inertia, Rotational Constants, Entropy, and Gibbs Free Energy of Rotation of a polyatomic molecule.
Help
Molecule atoms and coordinates in XYZ or MDL ".mol" format:

Temperature: K     Symmetry tolerance:     Force Rotation symmetry number:

Help:
• XYZ format consists of the first line with the number of atoms, the second line a comment, and succeeding lines with the x, y, z coordinates for each atom in angstroms. The coordinates can be separated by spaces, a tab, or a comma. List one x, y, z set per line.
• If the automatic point group recognition doesn't find the proper point group for your molecule, use a coarser setting for the "Symmetry tolerance." If you are not sure of the point group, you should try several different "symmetry tolerance" settings to make sure you find the highest symmetry.
• If the automatic point group recognition doesn't work, you can set the rotational symmetry number in the "Force Rotation symmetry number" dialog box.
• The Coordinates in Principal Coordinates Frame at the end of the listing aligns the molecule so that the axis with the largest principle moment of inertia lies along the x-axis. To see this orientation, copy and paste this section of the output into a text editor and save as a text only file with the extension ".xyz". Then open this file in your browser. The molecule will be displayed in a Chime window.
• The translational entropy uses a standard state of 1 bar. To find the translational entropy for a 1 atm standard state, subtract 0.1094 J mol-1 K-1 from the 1 bar value.
• The translational internal energy, U-U(0), is 3/2RT. The translational enthalpy is 5/2RT. The rotational internal energy is RT for a linear molecule and 3/2RT for a non-linear molecule. You can use the following table for the internal energy and enthalpy.
Internal Energy and Enthalpy of Translation and Rotation
Contribution of rotation alone (r) and translation and rotation (t+r) in kJ/mol.
 Linear Nonlinear U-U(0) r U-U(0) t+r H-H(0) t+r U-U(0) r U-U(0) t+r H-H(0) t+r T/K RT 5/2RT 7/2RT 3/2RT 3RT 4RT 100 0.8315 2.0786 2.9101 1.2472 2.4944 3.3258 200 1.6629 4.1573 5.8202 2.4944 4.9887 6.6516 298.15 2.4790 6.1974 8.6764 3.7185 7.4369 9.9159 300 2.4944 6.2359 8.7302 3.7415 7.4831 9.9774 310 2.5775 6.4437 9.0212 3.8662 7.7325 10.3100 310.15 2.5787 6.4469 9.0256 3.8681 7.7362 10.3150 400 3.3258 8.3145 11.6403 4.9887 9.9774 13.3032 500 4.1573 10.3931 14.5504 6.2359 12.4718 16.6290 1000 8.3145 20.7863 29.1008 12.4718 24.9435 33.2580

Colby College Chemistry, T. W. Shattuck, 6/28/2011