This transition moment type must be used for multiphoton or
Raman transitions and is
It is also appropriate for single photon transitions
classified as parallel or perpendicular. 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:
<stateA
|
μ| stateB
> =<stateA
|
T(
k,
|q|) +
T(
k,
-|q|)| stateB
>
and where it decreases is:
<stateA|
μ| stateB> = <stateA|T(k,|q|) - T(k,-|q|)| stateB>
The +
q and -
q
components are not necessarily symmetry related and two numbers are in
general required for
q
≠
0. Whether a paricular value of
q contributes to a spectrum depends on the symmetry of the states involved. (The value of
|q| gives the
allowed change in
K.)