Infrared spectrum condensed phase

The blue colour of oxygen in the liquid and solid phases is due to electronic transitions by which molecules in the triplet ground state are excited to the singlet states. These transitions are normally forbidden in pure gaseous oxygen and, in any case, they occur in the infrared region of the spectrum at 7918 cm" ( Ag) and 13 195 cm" ( ]+). However, in the condensed phases a... 

Molecules vibrate at fundamental frequencies that are usually in the mid-infrared. Some overtone and combination transitions occur at shorter wavelengths. Because infrared photons have enough energy to excite rotational motions also, the ir spectrum of a gas consists of rovibrational bands in which each vibrational transition is accompanied by numerous simultaneous rotational transitions. In condensed phases the rotational stmcture is suppressed, but the vibrational frequencies remain highly specific, and information on the molecular environment can often be deduced from Unewidths, frequency shifts, and additional spectral stmcture owing to phonon (thermal acoustic mode) and lattice effects. 

Having condensed the desired component in a trap it has to be decided whether to record the spectrum in the vapour state (method 1 below) or the liquid phase (method 2 next). Bellamy s method [113] is retained for identifying all components that, from the gas-chromatographic evidence, would appear to boil below 60 "C. Small amounts of such substances in liquid form are readily lost by vaporisation in attempting the transfer to a small liquid infrared cell. 

---