This implies that the kinetic translational energy dominates over rotational and vibrational molecule energies. Infrared spectroscopy is not the only method of studying molecular vibrational spectra. Absorption bands in the infrared are due to modes of vibrational excitation in water vapor. Vibronic spectra involve simultaneous changes in the vibrational and electronic energy states of a molecule. The energy difference corresponds to absorbed vibrational energy. In rovibronic coupling, electron transitions are simultaneously combined with both vibrational and rotational transitions. Molecules can also undergo transitions in their vibrational or rotational energy levels. Electronic transitions of gaseous molecules will show both vibrational and rotational fine structure. Thermal radiation is a byproduct of the collisions arising from various vibrational motions of atoms. Fluorescence spectroscopy is primarily concerned with electronic and vibrational states. The constituent molecules of a vapor possess vibrational, rotational, and translational motion. In other words, ionization is accompanied by vibrational excitation. The first exploits the selectivity of vibrational spectroscopy. The second formula is adequate for small values of the vibrational quantum number. The remaining degrees of freedom correspond to molecular vibrational modes.