"Vibrational modes" refers to the different patterns or ways something can vibrate. It describes how an object or system moves or oscillates when it is disturbed or excited. Full definition
The water molecule has a permanent dipole moment which gives it a rotational mode that has an effect on most of the IR spectrum radiated by the Earth as well as vibrational modes that only operate on specific wavelengths. (judithcurry.com)
But if the diamonds behaved as quantum mechanical objects, they would share one vibrational mode between them. (newscientist.com)
«The recorded images map the unique interaction between the different vibrational modes of the molecule and the varying enhanced electric fields sustained at different positions of the microscope's tip,» said Dr. Wayne P. Hess, a PNNL chemical physicist and co-author of the study. (pnnl.gov)