Calculation of Predissociation Rates of the B 3Π+u State of I2

Abstract

A comparison of the purely radiative decay rates of vibrational levels of the $B^3{\Pi }_{0^{+}u}$ state of I₂ with total decay rates obtained from several independent lifetime measurements has indicated a significant amount of spontaneous predissociation of the $B$ state. We present here a calculation of the observed relative predissociation rates by means of a model consisting of a repulsive $1_u$ state which is coupled to the $\mathrm{\upsilon \prime J\prime }$ levels of the $B$ state by rotational and electronic angular‐momentum terms neglected in the zeroth‐order Hamiltonian. The heterogeneous predissociation rate between a bound $\mathrm{\upsilon \prime J\prime }$ level and a continuum level at the same energy is calculated from Kronig's theory using exact wavefunctions for both levels. The dependence of this rate on the rotational level $\mathrm{J\prime }$ is taken into account, together with the fractional population of the $\mathrm{\upsilon \prime J\prime }$ levels which were excited in the measurement of the total decay rates. Excellent agreement is found between the calculated and observed relative predissociation rates at regions about $\mathrm{\upsilon \prime }$ of 14, 25, and 50 of the $B$ state for one position of the repulsive state lying very near the repulsive wall of the $B$ state over the energy range 17 300–20 000 cm⁻¹. The position of this state relative to the $B^3{\Pi }_{0^{+}u}$ and $A^3{\Pi }_{\text{1u}}$ states agrees well with Mulliken's prediction of the location of the ${}^1{\Pi }_{\text{1u}}$ state of I₂.