Lambda-doubling in the C1Π u state of H 2

The Λ-doubling of the H₂C¹Π _u state rovibronic energy levels by interaction with the B ¹Σ_u⁺ state is calculated. The present calculation seeks to improve on the similar work of Julienne ( 1) in three respects (1) The pure precession approximation is not made. (2) Stwalley's B-state potential curve ( 8) is used and the B- and C-state zero-order eigenvalues are more accurately positioned. (3) The effect of the B-state vibrational continuum is included. The Λ-doubling values agree with experiment to within 1.0 cm ^-1 for J = 1, 2, and 3, and to within 1.5 cm ^-1 for J = 4 and 5. It is shown that the Λ-doubling coupling matrix elements provide a sensitive test of electronic potential energy curves. In particular, the inaccuracy of the left limb of the B-state RKR curve is demonstrated.