Abstract: A new spectroscopic technique and corresponding spectrometer for molecules in which optical radiation is used to shift the rotational/nuclear-spin energy levels of freely rotatable sample molecules, and in which these shifts are detected using probing radiation. This technique enables the determination of individual polarizability components and/or combinations of these and/or information about the constitution of a sample that follows from these. In particular, it can reveal the enantiomeric constitution of a chiral sample whilst yielding a non-vanishing signal even for a racemate. The technique may find particular use in the analysis of molecules that are chiral by virtue of their isotopic constitution and molecules with multiple chiral centres.