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VUV photoabsorption spectrum of dimethyl carbonate in the energy region 7–11 eV and its complete spectral analysis with the aid of quantum chemical calculations is reported for the first time. The spectrum recorded using synchrotron radiation comprises of weak bands overlapping a broad intense continuum. With a view to interpret possible vibronic structure, gas phase infrared spectrum in the region 500–4000 cm −1 is revisited. Density functional theory (DFT) and time dependent DFT (TDDFT) methodologies are used to obtain ground state geometry, vibrational frequencies and vertical excitation energies of dimethyl carbonate. The intense broad features in the spectrum could be attributed to valence transitions. Based on quantum defect calculations, energy ordering and symmetry, weak bands are designated as ns, np and nd type Rydberg transitions converging to the first five ionization potentials. The highest occupied molecular orbital is nonbonding in nature and largely localized on the oxygen atom of carbonyl group and quantum defect values obtained are consistent with excitation from oxygen lone pair. Excellent correlation is obtained between theoretically predicted (CAM-B3LYP levels of theory) and experimentally observed excited state energies. Potential energy curves of ground and first few excited states generated with a view to provide additional insights into their nature and further describe the observed spectra. The present study provides a comprehensive experimental and computation analysis of the VUV photoabsorption spectroscopy of dimethyl carbonate. [ABSTRACT FROM AUTHOR]

The electronic spectra of diethyl carbonate (DEC) based on photoabsorption spectroscopy using synchrotron radiation are investigated in the 6.8-11.5 eV region. The VUV photo absorption spectrum reported here for the first time comprises broad features in the 7-11 eV region with few weak overriding spectral peaks. The broad peaks could be assigned to valence excitations, while the weak ones correspond to the Rydberg series of ns, np, and nd types, thus converging to the first five ionization potentials. Quantum defect values obtained are consistent with the excitation of an electron from oxygen lone pair. Infrared bands of DEC were revisited in the 600-3100 cm −1 region. The observed infrared bands of DEC could be assigned by DFT calculations. The TDDFT methodology is used to compute the vertical excited state energies, valence/Rydberg nature, and oscillator strengths of the excited electronic states. A good agreement using the CAM-B3LYP level of theory is achieved between the theoretically predicted values and experimental observations. In the ionic limit of DEC, the lengthening of the C O and CO–C 2 H 5 bond lengths is predicted. The potential energy curves of the first few excited states assisted in additional insights on the nature of the excited states and their role in photo dissociation dynamics. This study gives a first comprehensive report on the analysis of absorption spectra of DEC in the VUV region and the complete spectral assignments in the VUV and IR regions by quantum chemical calculations. [ABSTRACT FROM AUTHOR]

• VUV absorption spectrum of nitromethane, 9–11.8 eV region reported for first time. • First report of detailed spectral analysis aided by quantum chemical calculations. • Identification of 3rd IP at 11.95 eV by theoretical calculations and Rydberg analysis. • IR spectrum revisited, a few new combination and overtone bands assigned. • New insights into photodissociation dynamics by simulation of excited state PECs. A comprehensive spectroscopic study of the UV–VUV photoabsorption spectrum of nitromethane in the energy region 5.4–11.8 eV (43,500–95,000 cm−1) using synchrotron radiation is presented; the VUV absorption spectrum in the region > 9 eV being reported for the first time. The observed spectral features are assigned to various valence and Rydberg transitions, supported by quantum chemical calculations using the TDDFT method. The 6 eV region is dominated by a broad, intense absorption band peaking at ∼ 6.2 eV assigned to the π-π* valence transition, followed by rich Rydberg series converging to the first four ionization potentials of nitromethane. Theoretical calculations of orbital energies as well as Rydberg series analysis indicate that the third IP is located at 11.95 eV, in contrast to the earlier estimated value of 11.5 eV. Series of bands attributed to vibrational transitions accompanying the 3s (6a″), 3p(6a"), 3s(10a′) and 3s(5a″) Rydberg transitions are observed in the 60,000–73,000 cm−1 region and are tentatively assigned to progressions involving the NO 2 in-plane rock and CH 3 asymmetric deform modes. The liquid phase IR spectrum is revisited and assigned with the help of DFT calculations. A few new bands are observed and assigned to overtone and combination modes. Theoretically simulated potential energy curves of the first few excited singlet and triplet states with respect to the CN and NO bond lengths are useful in explaining some of the incompletely understood features of the photodissociation dynamics of nitromethane. It is found that direct dissociation in the Franck Condon region is a possible mechanism for the CH 3 NO + O channel, while singlet-triplet crossings play an important role in CN and NO bond scissions. [ABSTRACT FROM AUTHOR]

• First report of VUV spectrum in 7 – 11.5eV energy region. • Electronic spectrum assigned to valence and Rydberg series converging to first four ionization potential aided with quantum chemical stimulations. • First report predicted of fundamental vibrational modes and assignment of infrared spectra in 5004000 cm−1 region. • Interpretation of diffuse electronic spectra from study of low lying potential energy curves. A detailed spectroscopic study on ethyl methyl carbonate, a green solvent, has been carried out by recording vacuum ultraviolet and infrared spectra. The vacuum ultraviolet photoabsorption spectrum is recorded using synchrotron radiation from Photophysics beamline at the Indus-1 synchrotron radiation source at RRCAT, Indore, India in the wavelength region of 7–11.5 eV. Infrared spectra in gas phase as well as matrix isolated case are recorded using an indigenously developed laboratory low temperature experimental facility and a Fourier transform infrared spectrometer in the 500–4000 cm−1 region. Geometry optimization, vibrational frequency analysis of neutral & ionized ethyl methyl carbonate and electronic excited state energy information has been obtained using quantum chemical calculations. The observed ir spectral features could be assigned to the fundamental vibrational modes of the molecule. The vacuum ultraviolet region comprising a broad continuum is assigned to valence transitions having high oscillator strengths and overlying weak bands to ns, np, nd type Rydberg transitions. Potential energy curves of the ground and first few low lying excited states generated provided additional insights into their nature and further interpretation of observed experimental spectra. In this paper we report the first electronic absorption spectrum in 7 to 11.5 eV region, its spectroscopic analysis and identification of vibrational modes in the infrared spectra for ethyl methyl carbonate. Results of quantum chemical simulations carried out to obtain nature of excited states, energies and vibrational frequencies using GAMESS (USA) quantum chemistry code are also reported in this paper. [ABSTRACT FROM AUTHOR]

• UV–VUV (4.5–11.8 eV) photoabsorption studies of anisole using synchrotron radiation. • DFT/TDDFT calculations of ground & excited states correlated with observed spectra. • Comprehensive spectral analysis performed; first report of spectrum above 7.8 eV. • IR spectrum reinvestigated; new combination/overtone bands in1700–2700 cm−1 region. • UV photodissociation dynamics reinvestigated using simulated potential energy curves. Photoabsorption studies on anisole (C 6 H 5 OCH 3) are performed in the UV–VUV region (4.5–11.8 eV) using synchrotron radiation; the absorption spectrum in the region > 7.8 eV is reported here for the first time. Quantum chemical calculations are carried out on ground and excited states of anisole using the DFT and TDDFT methodologies and compared with experimental spectra in order to interpret the observed features in terms of the transitions involved, their valence/Rydberg nature and relative intensities. In order to validate the ground state spectral parameters, the infrared spectrum is recorded and assigned in the 600–3500 cm−1 region; a few new vibrational bands observed in the 1700–2700 cm−1 region are assigned to overtone and combination modes. The electronic absorption spectrum in the 4.5–5.0 eV region shows an extensive vibrational progression belonging to the first valence (ππ*) transition, while the 5.0–7.0 eV region is dominated by a broad and intense band peaking at ~6.6 eV which is assigned to two strong overlapping valence transitions originating from the HOMO–1 orbital. Additionally, throughout the 5.0–11.8 eV region, diffuse bands are observed which are attributed to Rydberg series (ns, np and nd) converging to the first four IPs of anisole. Theoretically simulated potential energy curves of ground and first few excited singlet and triplet states help in achieving a better understanding of the spectral features and the UV induced photodissociation mechanisms of anisole. The present studies suggest that photon excitation at 248 nm is likely to result in direct dissociation along a repulsive excited state (3s) in contrast to earlier studies which have attributed it to internal conversion to the ground state. [ABSTRACT FROM AUTHOR]