AB-INITIO STUDY OF NO2 - VII - (A)OVER-TILDE(2)B(2)[-(X)OVER-TILDE(2)A(1) NONADIABATIC FRANCK-CONDON ABSORPTION-SPECTRUM

We have calculated the nonadiabatic Franck-Condon cold absorption spec trum of the (X) over tilde(2)A(1)/(A) over tilde(2)B(2) conical inters ection of NO2, up to 22000 cm(-1). The role of the (A) over tilde(2)B( 2) Fermi polyads (upsilon(1), upsilon(2), 0) has been pointed out, bot h within and beyond the Born-Oppenheimer approximation. The diabatic a nd nonadiabatic results have been compared, both between themselves an d with experimental results. We have shown that the nonadiabatic inter actions give rise to a weaker and more chaotic intensity distribution, by mixing bright and dark states, by splitting the polyads into their multiplets, and by overlapping different polyads. The intensity maxim a therefore correspond to the (A) over tilde(2)B(2) (1, upsilon(2), 0) character of the nonadiabatic states up to 15000 cm(-1) (upsilon(2) = 5), and to more chaotic (A) over tilde(2)B(2) symmetric stretch-bendi ng progressions of the nonadiabatic bands at higher energies. The surv ival probability of the initial Franck-Condon state has been calculate d for three different sets of nonadiabatic states. The results in the energy and time domains nicely supplement and confirm each other, and highlight the beginning of the quantum chaos at about 16500 cm(-1) and its full development above 17500 cm(-1). (C) 1997 Elsevier Science B. V.