Probing the interaction between solid benzene and water using vacuum ultraviolet and infrared spectroscopy

Abstract

We present results of a combined vacuum ultraviolet (VUV) and infrared (IR) photoabsorption study of amorphous benzene : water mixtures and layers to investigate the benzene-water interaction in the solid phase. VUV spectra of 1 : 1, 1 : 10 and 1 : 100 benzene : water mixtures at 24 K reveal a concentration dependent shift in the energies of the 1B2u, 1B1u and 1E1u electronic states of benzene. All the electronic bands blueshift from pure amorphous benzene towards gas phase energies with increasing water concentration. IR results reveal a strong dOH-π benzene-water interaction via the dangling OH stretch of water with the delocalised π system of the benzene molecule. Although this interaction influences the electronic states of benzene with the benzene-water interaction causing a redshift in the electronic states from that of the free benzene molecule, the benzene-benzene interaction has a more significant effect on the electronic states of benzene. VUV spectra of benzene and water layers show evidence of non-wetting between benzene and water, characterised by Rayleigh scattering tails at wavelengths greater than 220 nm. Our results also show evidence of benzene-water interaction at the benzene-water interface affecting both the benzene and the water electronic states. Annealing the mixtures and layers of benzene and water show that benzene remains trapped in/under water ice until water desorption near 160 K. These first systematic studies of binary amorphous mixtures in the VUV, supported with complementary IR studies, provide a deeper insight into the influence of intermolecular interactions on intramolecular electronic states with significant implications for our understanding of photochemical processes in more realistic astrochemical environments.

VUV spectroscopy of an electron irradiated benzene : carbon dioxide interstellar ice analogue

“…From previous studies 24,30 we know that when solid-phase benzene is diluted with amorphous solid water a blueshi in the electronic bands compared to that of pure benzene is observed. We therefore used an unirradiated control sample to characterise the 1 : 100 C 6 H 6 : CO 2 mixture and any effects annealing might produce, the results of which are discussed in Section 3.1.…”

“…Interestingly the benzene band assignments for the 1 : 100 C 6 H 6 : CO 2 mixture are in good agreement with a 1 : 100 C 6 H 6 : H 2 O mixture. In the previous study by Dawes et al 30 several ratios (1 : 1, 1 : 10 and 1 : 100) of C 6 H 6 : H 2 O were studied and as the benzene was diluted, successive blueshis from pure benzene were observed and attributed to a matrix isolation effect. Also, the 1 : 100 C 6 H 6 : H 2 O mixture showed Table 1.…”

A new technique for determining the refractive index of ices at cryogenic temperatures

“…Initially, RAIRS was used to characterise the ices grown on HOPG. Infrared spectra of C 6 H 6 42,44,45,48,52,68,69 , MF [70][71][72][73][74][75] and H 2 O 42,43,56,[76][77][78] ices have all been recorded previously and are used as a benchmark for the spectra presented here. Figure 4 shows several RAIR spectra of C 6 H 6…”

Systematic investigation of CO2 : NH3 ice mixtures using mid-IR and VUV spectroscopy – part 1: thermal processing

“…Rayleigh scattering tails have been observed in VUV spectra of several astrophysical ices which did not fully wet the substrate and provided information on the morphology of the ice. 26,27 Rayleigh scattering tails were observed in the VUV thermal processing spectra (Fig. 7-9).…”