We present non-Born-Oppenheimer quantum-mechanical calculations of the behavior of isolated molecules of the ${\mathrm{H}}_2$ isotopomer series in static electric fields. Some conceptual aspects of such calculations are discussed. The values for polarizabilities and hyperpolarizabilities of the ${\mathrm{H}}_2$ isotopomers which we present are the first ever fully nonadiabatic calculated values of these properties.

• Received 21 May 2002

DOI:https://doi.org/10.1103/PhysRevLett.89.073001