Knowledge Bank

The high instantaneous pumping powers available in mode-locked 531 nm SHG and 354 nm THG pulses from $Nd3+$:glass lasers permit the study of fluorescences From excited states in photoreactive molecules which are so short-lived that they have escaped prior detection. We have characterized the spectra and fluorescence lifetimes in organic photoreagents (e.g., transazobenzene), small molecules (e.g., $I2$ in $CCl4$), and coordination compounds such as $ Mn_{2} (CO){10}$. Interesting trends are observed in the transition from resonance Raman emission (RRE) to fluorescence when picosecond excitation pulses are used. In favorable cases (e.g., in $B\to X$ fluorescence of $I2$ in $CCI{4} $), the emission spectrum can be used to infer the nature of competition between vibrational relaxation and photoreaction in the emitting state.