Issue 40, 2017

Vacuum ultraviolet photoabsorption spectroscopy of crystalline and amorphous benzene

Abstract

We present the first high resolution vacuum ultraviolet photoabsorption study of amorphous benzene with comparisons to annealed crystalline benzene and the gas phase. Vapour deposited benzene layers were grown at 25 K and annealed to 90 K under conditions pertinent to interstellar icy dust grains and icy planetary bodies in our solar system. Three singlet–singlet electronic transitions in solid benzene correspond to the 1B2u, 1B1u and 1E1u states, redshifted by 0.05, 0.25 and 0.51 eV respectively with respect to the gas phase. The symmetry forbidden 1B2u1A1g and 1B1u1A1g transitions exhibit vibronic structure due to vibronic coupling and intensity borrowing from the allowed 1E1u1A1g transition. Additionally the 1B2u1A1g structure shows evidence of coupling between intramolecular vibrational and intermolecular lattice modes in crystalline benzene with Davydov crystal field splitting observed. The optically forbidden 0–0 electronic origin is clearly visible as a doublet at 4.69/4.70 eV in the crystalline solid and as a weak broadened feature at 4.67 eV in amorphous benzene. In the case of the 1B1u1A1g transition the forbidden 0–0 electronic origin is only observed in crystalline benzene as an exciton peak at 5.77 eV. Thicker amorphous benzene samples show diffuse bands around 4.3, 5.0 and 5.4 eV that we tentatively assign to spin forbidden singlet–triplet 3B2u1A1g, 3E1u1A1g and 3B1u1A1g transitions respectively, not previously reported in photoabsorption spectra of amorphous benzene. Furthermore, our results show clear evidence of non-wetting or ‘islanding’ of amorphous benzene, characterised by thickness-dependent Rayleigh scattering tails at wavelengths greater than 220 nm. These results have significant implications for our understanding of the physical and chemical properties and processes in astrochemical ices and highlight the importance of VUV spectroscopy.

Graphical abstract: Vacuum ultraviolet photoabsorption spectroscopy of crystalline and amorphous benzene

Article information

Article type
Paper
Submitted
05 Aug 2017
Accepted
28 Sep 2017
First published
28 Sep 2017

Phys. Chem. Chem. Phys., 2017,19, 27544-27555

Vacuum ultraviolet photoabsorption spectroscopy of crystalline and amorphous benzene

A. Dawes, N. Pascual, S. V. Hoffmann, N. C. Jones and N. J. Mason, Phys. Chem. Chem. Phys., 2017, 19, 27544 DOI: 10.1039/C7CP05319C

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements