Making a Linear Molecule Data File
A simple linear
molecule file can be generated from File, New, Linear Molecule.
This initializes the program for a molecule with a band origin of 1000
cm-1and B' = B'' = 1 cm-1. To adjust
the constants (and set the type of vibronic transition) use select View, Constants.
Most constants and settings can be left unchanged at their default
values (and indeed should be unless you need a specific effect) but the
ones that must normally be changed are adjusted as follows:
- If the molecule has a centre of symmetry, click on "Linear
Molecule" and set Symmetric
= "True". You will also
need to set the statistical weights in the same
window. For diatomic molecules with nuclear spin I the values should be:
|
I integral
|
I
half integral
|
SymWt |
(I+1)(2I+1) |
I(2I+1) |
AsymWt |
I(2I+1) |
(I+1)(2I+1) |
Note that you should leave nNuclei at 0 unless you
specifically want to calculate hyperfine structure.
- Adjust the ground state by clicking on the "v=0" entry under
"Ground". The key things
to set are:
- Lambda (to Sigma+, Sigma-, Pi, Delta, ...)
- Overall electronic Spin, S.
- If the molecule is symmetric, set gerade
(True for g, False for u)
- The rotational constant, B
- For non Σ states, the spin orbit coupling constant, A.
- For S ≥ 1 LambdaSS (the spin-spin
coupling constant) may also be important.
- Now switch to the upper state (click on the "v=1" entry under "Excited") . The key things to
set here are:
- The Origin
- All the settings and values listed above under the ground state.
- The
(spherical) transition moment
may also need adjusting,; the default is for a standard one photon
electric dipole transition. See here for Raman
or multiphoton transitions.
For details of the Hamiltonian used, see the section on the Linear Molecule Hamiltonian.