Ágúst Kvaran*, Benedikt G. Waage and Huasheng Wang
Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavík, Iceland
Hönl-London type approximation expressions are derived for transition
strengths of the W´=0,1,2,3, <- W"=0
(S,P,D and F <-
S) three photon transitions for diatomic molecules
belonging to Hund´s case (a) and intermediate (a)-(b) coupling schemes.
These are used to demonstrate what may be seen and what may not be seen
in three photon absorption spectra. The forms are used to simulate room
temperature (3+1)REMPI spectra of HBr, for different electronic transitions.
The analysis as well as comparison with (2+1)REMPI spectra is used to demonstrate
the usefulness of three photon absorption spectroscopy to identify excited
states and to derive spectroscopic parameters. A Rydberg state, not
observed in single or two photon absorption, with band origin
82837 cm-1 was identified and analysed for the first time. It
was assigned as the L1F(3) ((s2p3)5dd))
state, (0,0) band.