Spherical Transition Moment

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:
T(k,q) = <stateA, Λ+q| μ | stateB, Λ>
where k is the "Rank" and q the "Component" setting, normally chosen to be >= 0. The corresponding matrix element:
T(k,-q) = <stateA, Λ-q| μ | stateB, Λ>
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:
<stateA| μ| stateB> = T(k,|q|) + T(k,-|q|)
and where it decreases is:
<stateA| μ| stateB> = T(k,|q|) - T(k,-|q|)

Settings

Rank Rank of transition -1 for a normal electric dipole transition; see here for multiphoton or Raman transitions
Component Projection quantum number of transition moment. The default is auto, which for simple cases implies taking the only value of the component which gives an allowed transitions. In the standard one photon case it will be 0 for a parallel transition and 1 for a perpendicular transition. For more complicated cases auto will not work and a specific component must be taken.

Parameters

Strength Transition (dipole) moment. For one photon transitions this has units of Debye. Note that the relative intensity is proportional to the square of this value.
C J dependence of transition moment
D J dependence of transition moment