This transition moment can be used
for any molecule type, and must be used for multiphoton or
Raman transitions.
It is also appropriate for single photon transitions
classified as parallel or perpendicular, as noted below. For linear
molecules the "Strength" number is the value of the vibronic only
matrix element:
is then computed by symmetry. The
order of the states (which can be significant in cases involving
multiple transition moments) is as displayed in the constants window.
Strictly all the above matrix elements should have selection rules Δ S
= 0 (and Δ Σ = 0 for linear molecules), but as an extension
PGOPHER relaxes this
requirement for Δ S ≠ 0 transitions and only enforces the
|Δ Ω| =
q rule. See the
section on
Forbidden Transitions in Linear
Molecules for a more detailed discussion of this.
Symmetric tops are similar, though the states are
then labeled by
symmetry rather than Λ.
(The value of
|q| gives the
allowed change in
K.) For
asymmetric tops the situation is more complicated as the +
q and -
q
components are not necessarily symmetry related and two numbers are in
general required for
q
≠
0. The "Strength" numbers are actually taken as the sum and
difference of the two components such that the value of the vibronic
matrix element where
K
increases is: