The 3d Rydberg state of the BeH molecule

The absorption and the emission spectra of the BeH and BeD molecules in the region of 1850 Å are rotationally analysed. The features observed are shown to correspond to a transition between the X 2Σ+ ground state and a 3d molecular complex that is strongly predissociated by the C 2Σ+ state. Rotational constants for the v = 0 and v = 1 levels of the 3d state are derived by matrix diagonalization techniques, assuming interaction with the F(4pσ) 2Σ+ state. A tentative assignment of previously observed absorption bands to transitions involving the v = 2 level of the 3d state is given. The 2-0 band of the B 2Π-X 2Σ+ transition of BeH and BeD is also identified in this region. The predissociation by the C 2Σ+ state is discussed.