Infrared radiative decay dynamics from the γ 1u ((3)P2), H 1u ((3)P1), and 1u ((1)D2) ion-pair states of I2 observed by a perturbation facilitated optical-optical double resonance technique.

We report the spectroscopic and temporal analyses on the amplified spontaneous emission (ASE) from the single rovibrational levels of the Ω = 1u ion-pair series, γ 1u ((3)P2), H 1u ((3)P1), and 1u ((1)D2), of I2 by using a perturbation facilitated optical-optical double resonance technique through the c (1)Πg ∼ B (3)Π(0u (+)) hyperfine mixed valence state as the intermediate state. The ASE detected in the infrared region was assigned to the parallel transitions from the Ω = 1u ion-pair states down to the nearby Ω = 1g ion-pair states. The subsequent ultraviolet (UV) fluorescence from the Ω = 1g states was also observed and the relative vibrational populations in the Ω = 1g states were derived through the Franck-Condon simulation of the intensity pattern of the vibrational progression. In the temporal profiles of the UV fluorescence, an obvious delay in the onset of the fluorescence was recognized after the excitation laser pulse. These results revealed that ASE is a dominant energy relaxation process between the Ω = 1u and 1g ion-pair states of I2. Finally, the lifetimes of the relevant ion-pair states were evaluated by temporal analyses of the UV fluorescence. The propensity was found which was the longer lifetime in the upper level of the ASE transitions tends to give intense ASE.