Preferred Label : transition (dipole) moment;
IUPAC definition : An electromagnetic wave may induce an oscillating electric moment in a molecule (possibly
leading to absorption if the oscillation frequency is equal to the light frequency).
The amplitude of this moment is the transition moment between the initial (i) and
final (f) states (here assumed to be non-degenerate): \[M_{{if}} \, {f} \mid M_{{op}}\mid
{i} \] where Mop is the electric dipole moment operator, a vector operator that is
the sum of the position vectors of all charged particles weighted with their charge.
The transition moment Mif is a vector in the molecular framework, characterized both
by its direction and its probability.;
Scope note : it is frequently said that a transition is polarized along the direction of its transition
moment and this direction is called the polarization direction of the transition.; the absorption probability for linearly polarized light is proportional to the cosine
square of the angle between the electric vector of the electromagnetic wave andmif;light
absorption will be maximized if they are parallel, and no absorption will occur if
they are perpendicular.; in the case of a vibronic transition, where both the initial and the final states
may be characterized by (different) electronic and vibrational states, the franck–condon
principle is often applied. this approximation separates electronic and nuclear descriptions
and allows the transition moment to be written as a product of a purely electronic
transition moment and an overlap integral between the two vibrational wavefunctions
involved.; in the case of a doubly degenerate final state f, each of the two components at the
same energy has a transition moment and the two moments define a plane. the transition
is then said to be polarized in that plane, which also defines its polarization direction(s).
this is typically the case for some of the transitions in highly symmetrical molecules.;
Origin ID : T06460;
See also
An electromagnetic wave may induce an oscillating electric moment in a molecule (possibly
leading to absorption if the oscillation frequency is equal to the light frequency).
The amplitude of this moment is the transition moment between the initial (i) and
final (f) states (here assumed to be non-degenerate): \[M_{{if}} \, {f} \mid M_{{op}}\mid
{i} \] where Mop is the electric dipole moment operator, a vector operator that is
the sum of the position vectors of all charged particles weighted with their charge.
The transition moment Mif is a vector in the molecular framework, characterized both
by its direction and its probability.
