Electronic quenching of I2 B 3Π(0+u) by He at low collision energies

Electronic quenching of I2 B 3Π(0+u), v′=11 by He has been investigated in a free jet expansion. The quenching cross section was found to be 0.33±0.08 Å2 at 9.4 K, which is significantly smaller than the room temperature value (0.89±0.02 Å2). The temperature dependence of the cross section has been quantitatively characterized in terms of a collision induced predissociation model. Calculations based on this model show that the predissociation is induced by dispersion forces acting between the collision partners, and they provide information about the symmetry of the repulsive state involved. The calculations are also shown to be compatible with the predissociation and fluorescence decay dynamics of the HeI2 (B) van der Waals complex.