Born-Oppenheimer breakdown effects from rotational analysis of the A(1)Sigma(+)-X(1)Sigma(+) band system of BeH+, BeD+, and BeT+

The A(1) Sigma(+) - X(1) Sigma(+) band system of BeH+, BeD+, and BeT+ has been photographed at high resolution and rotationally analyzed. Together with literature data (W. W. Watson and R. F. Humphreys, Phys. Rev. 52, 318-321 (1937)) for upsilon'' = 7-10 of BeH+, the data set samples vibrational levels that extend up to approximate to 2/3 and approximate to 1/2 of the well depths of the X and A states, respectively. The measured line positions were employed in a global least-squares fit of the molecular Hamiltonians for the two states that take account of Born-Oppenheimer breakdown effects and in which a modified Lennard-Jones (MLJ) function is employed for the potential energy. The fit reproduces the measurements to within the estimated accuracy (approximate to 0.05 cm(-1)). (C) 1997 Academic Press, Inc.