Potential energy curves of ICl and non-adiabatic interactions studied by the spin-orbit CI method

Excited state potential curves of ICI have been obtained by the spin-orbit CI method to describe the non-adiabatic interactions. Variations of each wavefunction are analyzed and three avoided crossings are characterized between 0(+)(III)/0(+)(IV), 0(+)(II)/0(+)(IV), and 0(+)(II)/0(+)(III) at R = 2.85, 3.14 and 3.62 Angstrom, respectively. The second avoided crossing, that was suggested before by Tiemann et al. is proved here for the first time. Our (1)II(1), 1(II) state crosses with the B state just inside the second avoided crossing, supporting the experimental analyses made by Gordon et al. and Tiemann et al. Applying to the B state photodissociation, our potential curves yield the wavelength dependence of the branching ratios, I((2)P(3/2)) + Cl((2)P(3/2))/I((2)P(3/2)) + Cl((2)P(1/2)), in good agreement with experimental results. Photodissociation from the second absorption band is also discussed based on our theoretical and recent experimental results. (C) 1999 Elsevier Science B.V. All rights reserved.