Giant enhancement of high-order rotational and rovibrational transitions in near-field spectroscopy in proximity to nanostructures

Vibrational-rotational and pure rotational transitions usually occur only via the electric dipole interaction channel and some molecules, such as homonuclear diatomics, do not have an electric dipole moment, rendering them transparent to infrared spectrum. We show that resonant nanostructures result in giant enhancement of high-order transitions in a relatively large volume, which implies an observable infrared signature for these molecules. The enhancement of these transitions may find applications in imaging, tissue ablation, resolving chiral molecules, and studies of molecules that are challenging to detect.