The two-photon absorption spectrum of NO2 in the energy region from 55 000 to 60 000 cm-1 shows two new highly resolved band systems. The lower of these is recognized as the 3pσ 2Σu+ Rydberg state, higher members of which have been observed in previous work by conventional vacuum-UV absorption spectroscopy. The higher system is assigned to its companion 3pπ 2IIu Rydberg state, seen here for the first time. Both band systems evidence clear origins in bent-to-linear transitions, assignments which are confirmed by the rotational structure of individual bands. An important feature of these spectra is the high intensity of the origin and low-frequency cold bands, which deviates strongly from Franck-Condon predictions. We suggest that this behavior can be explained by intramolecular relaxation within the continuum of intermediate states resonant with the first photon.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry