The Effect of Temperature on the Absorption Bands of Benzene and Some of Its Derivatives at Low Temperatures

The ultraviolet absorption spectra of benzene and the derivatives, ortho, meta, and para dichlorbenzene, were investigated throughout the temperature range from -190^∘{}C to 20^∘{}C. The behavior of the spectra of the four compounds is very similar. They all show a number of unresolved major and minor absorption bands. Both the frequency and the intensity of these bands increase with a decrease of temperature. The temperature-frequency curves are all approximately represented by parabolic equations, except in the neighborhood of their melting points. The frequency difference between the bands remain constant with temperature within the limits of the experiment and agree favorably with those found by other spectroscopic methods. If these frequency differences are due to the vibrational transitions within the molecule, this spectral shift cannot be accounted for on the basis of a change in the inner vibrational terms, as has previously been suggested.