Knowledge Bank

The $B\to X$ fluorescence of $I2$ produced in the hindered photodissociation of $I2$ Ar at 488 nm has been resolved. The spectra show several vibrational progressions with low rotational energy, the most prominent of these is a $($\upsilon', D)$ progression extending from $\upsilon \prime =49$ to at least $\upsilon \prime =23$. The $I2$ Ar complexes were excited and the $I2$ fluorescence was observed under collisionfree conditions in a supersonic free-jet expansion. We attribute these observations to a one atom photodissociation cage effect in the $I2$ Ar complex, in which the molecular iodine, although excited more than $400cm-1$ above the B state dissociation limit, is prevented from dissociating by energy transfer to the argon atom, resulting in the breaking of the van der Waals bond, $I2Ar⟶488nm,I2(B)+Ar,$ leaving the iodine molecule in a bound level of the B electronic state, $386cm-1$ to $1889cm-1$ below the dissociation limit. Interpretation of the dynamics of the cage effect in terms of a simple impulsive energy transfer model will be presented.