Electronic spectroscopy of trans-2-hexenal and 3-hexanol: Experimental and computational studies

Abstract

Spectroscopic study of the absorption spectra of two green gases viz. trans-2-hexenal and 3-hexanol molecules by means of synchrotron radiation based photoabsorption and FTIR spectroscopy is presented. Quantum chemical calculations are used to compute the ground and excited state properties and correlate to the experimental results. From the IR spectra, vibrational assignments in the 600–3200 cm−1 region are made for the first time with the help of predicted fundamental frequencies at the optimized geometries for the molecule using DFT methodology. The electronic absorption spectra recorded in the 5.5–10 eV region for trans-2-hexenal consists of strong valence band at 6 eV followed by weak structures assigned to Rydberg series converging to the first two ionization potentials. While for 3-hexanol the electronic spectra lies entirely in the VUV region consisting of broad continuous absorption band above 7 eV. Vertical excited state energies are predicted using TDDFT calculations assist the assignments of the experimental electronic peaks to Rydberg and valence transitions. To get insights into the nature of the excited states potential energy curves of the first few excited states with respect to bond lengths and bond angles are studied. This work presents a first consolidated report of experimental and theoretical computation of photo absorption spectrum of trans-2-hexenal and 3-hexanol in the region IR and VUV absorption spectra.