g the following statements as they apply to infrared spectroscopy. Decide if each is true or false. For a given pair of atoms, the vibrational frequency expected if they are joined by a single bond should be higher than if they are joined by a double bond. Because molecules in condensed phases (solids and liquid) are not free to rotate, rotational-vibrational transitions are not observed in their infrared spectra. For this reason, even at high resolution, a condensed phase spectrum is characterized by broad bands. Absorption bands in infrared spectroscopy are due to electronic transitions in molecules. Heteronuclear diatomic molecules such as HCl do not absorb infrared radiation. Air contains nitrogen and oxygen - both of which strongly absorb infrared radiation. For this reason, most FTIR instrument are operated under vacuum.