Ultraviolet Absorption Spectra of Benzene and Chlorobenzene in Water-Ice Solutions at Temperatures Between 78 K and 273 K

In this paper, characteristic ultraviolet absorption spectra are presented for benzene and chlorobenzene in transparent hexagonal water–ice solutions at temperatures between 273 K and 78 K. In addition, the liquid solution spectra at 292 K have also been included. The two lowest symmetry-forbidden transitions from the ground state (1A1g) to the first excited level of symmetry (B2u), denoted as 1B2u ← 1A1g, and the transition from the ground state to the second excited level of symmetry (1B1u), denoted as 1B1u ← 1A1g, of benzene are recorded. The two lowest transitions of chlorobenzene from the ground state (1A1) to the first excited level of symmetry (1B2), denoted as 1B2 ← 1A1, and the transition from the ground state to the second excited level of symmetry (1A1) denoted as, 1A1 ← 1A1, are also studied. The bands are obtained for slowly cooled transparent water–ice solutions. Such ice samples, that were frozen from liquid water and cooled, show gradual changes in the spectra. Our study shows the spectra at eight temperatures, separating the spectra in different regions based on the range for the bands from ground state to the first and second excited states of benzene and chlorobenzene, observing changes in the integrated absorbances as a function of the temperature. For the spectra recorded at 78 K, the peak absorbances as a function of the wavelength are presented and tentatively assigned. Peak assignments are based on the known literature of benzene and chlorobenzene. The temperature range of our study covers some of the average temperatures that have been found in the icy moons of Saturn and the polar regions of Earth.