ASYMMETRIC ADIABATIC CORRECTION TO THE ROTATION-VIBRATION LEVELS OF H2D+ AND D2H+

Calculations on H2D+ and D2H+ have shown that the energy levels of these asymmetric isotopomers of H 3+ cannot be reproduced using effective potential energy surfaces with D3h symmetry. It is shown that for these ions the adiabatic correction to the Born-Oppenheimer approximation has an asymmetric component which can be expressed as a mass-independent surface multiplied by a mass factor. An expression for this function is obtained from ab initio calculations. Use of this adiabatic correction is found to resolve the discrepancy with the levels of H2D+ and D 2H+. The ab initio calculations reported reproduce the observed H2D+ transitions with an average error (obs-calc) of -8 MHz for the rotational transitions, -0.06 cm-1 for the v 1 band, -0.13 cm-1 for v2, and -0.19 cm -1 for v3. These errors are nearly constant for all transitions within a vibrational band. This gives a very accurate ab initio framework for predicting unobserved transition frequencies. © 1995 American Institute of Physics.