Knowledge Bank

We have recorded the dispersed fluorescence spectra of the linear and the previously well-studied T-shaped isomeric $ArI2$ complexes following $B\leftarrow X$ excitation. The dispersed fluorescence features originate from the free $I2B\to X$ emission and reveal the $I2$ product vibrational state distribution. The vibrational distribution of photofragment $I2(B)$ produced from dissociation of the T-shaped isomer shows a sharp Poisson distribution, beginning with $\Delta v\prime =-3$ which is nearly independent of excitation energy. The vibrational distribution of $I2(B)$ from the linear isomer is quite different. For excitation energies greater than that corresponding to $I2(B,v\prime =22)$, the product distribution is quite similar to that observed for excitation above the dissociation energy of the B state, i.e., it shows a broad, nearly gaussian distribution of $I2(B)$ vibrational states, well below the excitation energy. For excitation energies below that, the distribution becomes increasingly like the Poisson distribution observed for the T-shaped isomer. Bond dissociation energies for linear and T-shaped isomers are determined for the spectra. The dissociation time scale for the two isomers differs by about 3 orders of magnitude. To model the product state distribution of the linear isomer and therefore gain further insight into the $Ar-I2$ interaction potential, a simple trajectory calculation based upon the classical dynamics of a compressed oscillator (I-I) ejecting a freely attached particle (Ar) is in progress. Results from the calculation are in good accord with the experiment.