Molecule Types Asymmetric Tops Transition Moments | <Prev Next> |

This transition moment type must
be used for multiphoton or Raman
transitions. It is also appropriate for single photon transitions
classified as parallel or perpendicular. The notation used here is
slightly non-standard; 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
(taking q > 0):

_{2v}), so only one may be required. For
*k* = 1 the following identifications can be made:

<stateA, K+q| μ| stateB,
K> = T(k,q) + T(k,-q)

T(k,q) and T(k,-q) are the Strength parameters; they are not necessarily
symmetry related and two numbers are in general required for q ≠ 0. With this
definition the operators multiplying T(k,q) and T(k,-q)
will have often have different symmetries in more symmetric point
groups (such as Cand where it decreases is:

<stateA, K-q| μ| stateB, K> = T(k,q) - T(k,-q)

<stateA|making the three possible components approximately equivalent to the three Cartesian components, but with a different phase choice.z|stateB> =T(1,0)

<stateA|x|stateB> = -2^{½}T(1,-1)

<stateA|y|stateB> =i2^{½}T(1,1)

While the sign or phase of transition moment matrix elements is often irrelevant, it will be important if more than one transition moment can contribute to a given transition, either through multiple components for a single vibronic transition, or if different vibronic states are mixed, allowing interference between different pathways to the same final state. In such circumstances the relative signs are important and, given the definition above, the order in which states are specified will make a difference to the parameters required. Swapping the bra and ket over will change the sign of the T(k,-q) component.

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. For more complicated cases auto will not work
and the component must be specified. |

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. |