Rotational Constant Calculator
calculates the point group, Principal Moments of Inertia, Rotational Constants,
Entropy, and Gibbs Free Energy of Rotation of a polyatomic molecule.
Internal Energy and Enthalpy of Translation and Rotation
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
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
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
Contribution of rotation alone (r) and translation and rotation (t+r) in kJ/mol.
Colby College Chemistry, T. W. Shattuck, 6/28/2011