Experimental determination of the orientation of the molecular electric dipole moment within light molecules: A rotational zeeman effect study of H 2CO and D 2CO in excited vibrational states

Abstract

It is known since long that at least in principle the orientation of the molecular electric dipole moment within a light molecule may be determined from the change of its molecular g-tensor elements upon isotopic substitution. In formaldehyde however, this method has lead to large discrepancies and has cast some doubts on its usefulness, at least as long as vibrational effects are neglected. The results of the present investigation indicate that vibrational effects are indeed responsible for the discrepancies and should be accounted for especially if hydrogen-deuterium substitutions are involved. In the appendix we discuss the problem to which approximation the same molecular property, called dipole moment, is measured by a rotational Stark effect experiment and by a rotational Zeeman effect experiment.