Resonance coalescence in molecular photodissociation.

We study theoretically the photodissociation dynamics of the H_{2};{+} molecular ion exposed to a linearly polarized laser light. It is shown that it is possible to choose a laser wavelength and intensity so as to produce a coalescence of two photodissociation vibronic resonance states. At such a coalescence point, also called an exceptional point, the photodissociative resonance wave function is self-orthogonal. This unique phenomenon which is presented here for light induced molecular dynamics enables us to transfer completely the nondissociated molecules from one vibronic state to another by varying adiabatically the laser frequency and intensity along a closed contour which encircles the exceptional point.