- We report the results of a theoretical study of the vibrational shape resonances in the C1Πu state of H2. The adiabatic potential curve for the C1Πu state was used in a single-channel calculation of the resonance positions and widths; there is at most one shape resonance for each value of the rotational quantum number J. Then the two-channel problem of the C1Πu and B1Σu states coupled by the same nonadiabatic interaction (Born-Oppenheimer correction) that gives rise to the Λ-doubling of the bound levels of the C state was solved, to investigate the effects of this coupling on the shape resonances. Eigenphase trajectories versus continuum energy are presented; effects of the noncrossing rule are seen. Finally, we calculated the photoabsorption cross section in the vicinity of the shape resonances, both for specific J final states and also for cross sections summed over final state J values and averaged over initial J states assuming T = 300 K. © 1991.