Lifetime lengthening of molecular Rydberg states in the condensed phase

We report on fluorescence lifetime lengthenings of molecular Rydberg states in condensed media in the case of the NO molecule trapped in inert gas matrices. In rare gas matrices, the fluorescence of the A 2Σ+ state originates from two types of sites, hereafter called red and main. The red site is considered to be a loose site with more than one vacancy in Ar, Kr, and Xe and an h.c.p. site in Ne matrices. It exhibits a lifetime lengthening with respect to the gas phase of 25% in Kr matrices and 100% in Xe matrices. The main site fluorescence stems from monosubstitutional sites. It exhibits lifetime enhancements of up to 100% when going from Ne to Xe matrices. When, however, the fluorescence quantum yields are taken into account, the lifetime increases from the gas phase value to up to two orders of magnitude in the sequence H2–Ne(D2)–Ar–Kr–Xe. Furthermore, this change in transition moment is not observed in the absorption spectrum. These results stress the influence of the solvent and its microscopic structure on molecular Rydberg lifetimes. Different mechanisms are discussed in relation with the observations.