Experimental and theoretical studies on the absorption spectra of n-dodecane in the IR and VUV regions. (October 2019)

• Record Type: Journal Article
• Authors: Gorai, Kiran Kumar; Shastri, Aparna; Singh, Param Jeet; Jha, S.N.
• Is Part Of: Journal of quantitative spectroscopy & radiative transfer. Volume 238(2019)
• Publication Date: 2019-10
• Subjects: n-Dodecane -- Synchrotron radiation -- Infrared -- Vacuum ultraviolet -- TDDFT; Spectrum analysis -- Periodicals; Radiation -- Periodicals; Analyse spectrale -- Périodiques; Rayonnement -- Périodiques; Radiation; Spectrum analysis; Periodicals; 543.0858
• DOI: 10.1016/j.jqsrt.2019.106582
• Languages: English
• ISSNs: 0022-4073

Abstract

Highlights: Comprehensive IR and VUV photoabsorption studies of n-dodecane. DFT calculations of ground state geometry and vibrational frequencies. TDDFT calculation of vertical excited state energies & potential energy curves. Assignment/interpretation of observed IR & VUV spectra backed by calculations. First report of VUV absorption spectrum & TDDFT calculations of n-dodecane. Abstract: We report here a comprehensive spectroscopic study of the absorption spectrum of the n-dodecane molecule using synchrotron radiation based photoabsorption and FTIR spectroscopy. Quantum chemical calculations using the DFT and TDDFT methodologies are used to predict relevant ground and excited state properties and correlate them with the experimental results. In the IR spectrum, assignment of the prominent CH stretching bands in the 2800–3000 cm −1 region are consolidated while a few new vibrational assignments are made in the 700–1500 cm −1 region. The electronic absorption spectrum of n-dodecane lies entirely in the vacuum ultraviolet (VUV) region and consists of a broad continuous absorption band starting from ∼7.5 eV, with no discernible structure. TDDFT calculations of vertical excited states predict that most of the excited states are Rydberg in nature. Potential energy curves of the first few excited states with respect to various bond lengths and bond angles are studied in order to gain additional insights into the nature of the excited states. The broad nature of the absorption is attributed partly to the effect of several conformers as well as hot bands from low frequency modes in the ground state and partly due to overlap of several Rydberg series converging to the first few ionization potentials (IPs). Energy separation between the first and second IP is theoretically predicted to be ∼0.65 eV, while successive separation between the second, third, fourth and fifth IPs is ∼0.03 eV. To the best of our knowledge this is the first report of the VUV absorption spectrum of n-dodecane in the region from 6 to 10 eV, as also the first report of theoretical calculations of its electronically excited states.