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[Display omitted] • Detailed theoretical study of structural, spectroscopic and electron scattering cross section study of glycolaldehyde. • Quantum chemical calculations for ground and excited states are performed using DFT and TD-DFT methods. • In the absence of sufficient experimental data on excited states of glycolaldehyde, we compare VES calculations with the available experimental data for an analogous molecule acetaldehyde. • Maiden theoretical attempt to provide Low-energy (0.1 to 20 eV) scattering cross-sectional data using R-matrix method. • We have detected one π* shape resonance in all the three models viz. SE, SEP and CC model. Detailed theoretical investigations on structural, spectroscopic and electron scattering cross sections of glycolaldehyde, the first ever detected sugar in space are reported in this work. Spectroscopic calculations are performed on the ground and excited states of glycolaldehyde using density functional theory (DFT) and time-dependent density functional theory (TDDFT), respectively. The optimized geometrical parameters and vibrational spectrum are in good agreement with the earlier reported work. Vertical excited state (VES) energies at the TDDFT/B3LYP/aug-cc-PVQZ level of theory along with detailed assignments are reported up to 30 transitions. The TDDFT predicted Rydberg series energies are compared with the Rydberg series of glycolaldehyde converging to its first IP, computed using the standard Rydberg formula and are found to be in good agreement. In the absence of sufficient experimental data on excited states of glycolaldehyde, the theoretical results are validated by comparison of VES calculations performed at the same level of theory with the available experimental data for an analogous molecule viz. acetaldehyde. Triplet excited-state energies for glycolaldehyde are reported here for the first time. Electron impact cross section calculations in the energy range 0.1 to 20 eV are carried out using ab-initio R-matrix method. We have detected one π* shape resonance in all the three models viz. SE, SEP and CC, which may also lead to a possible fragmentation channel wherein a hydrogen atom is removed from the molecule forming a glycolaldehyde dehydrogenated anionic radical (C 2 H 3 O 2 −). The π* shape resonance is correlated with the corresponding molecular orbital electronic structure calculations. Additionally, differential, electronic excitation, ionization and total cross sections are reported here for the first time. [ABSTRACT FROM AUTHOR]

Computational studies of electronically excited states of the acetone molecule [(CH 3 ) 2 CO] and its fully deuterated isotopologue [(CD 3 ) 2 CO] are performed using the time dependent density functional (TDDFT) methodology. In addition to vertical excitation energies for singlet and triplet states, equilibrium geometries and vibrational frequencies of the n =3 Rydberg states (3 s , 3 p and 3 d ) are obtained. This is the first report of geometry optimization and frequency calculations for the 3 p x , 3 p z , 3 d yz , 3 d xy , 3 d xz , 3 d x 2 –y 2 and 3 d z 2 Rydberg states. Results of the geometry optimization indicate that the molecule retains approximate C 2V geometry in most of these excited Rydberg states, with the most significant structural change seen in the CCO bond angle which is found to be reduced from the ground state value. Detailed comparison of the computationally predicted vibrational wavenumbers with experimental studies helps to confirm several of the earlier vibronic assignments while leading to revised/new assignments for some of the bands. The important role of hot bands in analysis of the room temperature photoabsorption spectra of acetone is corroborated by this study. While the vibrational frequencies in excited Rydberg states are overall found to be close to those of the ionic ground state, geometry optimization and vibrational frequency computation for each excited state proves to be very useful to arrive at a consistent set of vibronic assignments. Isotopic substitution helps in consolidating and confirming assignments. An offshoot of this study is the interpretation of the band at ~8.47 eV as the π –3 s Rydberg transition converging to the second ionization potential. [ABSTRACT FROM AUTHOR]

• Comprehensive structural, spectroscopic and electron collision data of Isoxazole. • DFT calculations of ground state geometry and vibrational frequencies. • Comparison with earlier data; confirmation/revision of vibronic assignments. • Vertical excitation energies for singlet and triplet states using TDDFT. • Low energy electron scattering data for Isoxazole from 0.1-20 eV. The structural, spectroscopic, and electron collision data of Isoxazole (C 3 H 3 NO) were subjected to extensive computational studies. Spectroscopic calculations were performed on ground and excited states using the density functional theory (DFT) and the time dependent density functional theory (TDDFT) respectively. Ground state geometry and vibrational frequencies agree well with earlier works and lead to re-assignment of a few vibrational bands. Theoretically predicted singlet and triplet excitation energies are in good agreement with earlier experimental data, while predicted oscillator strengths of singlet states correlate well with the observed relative spectral intensities. The electron collision data for isoxazole molecule were calculated using Quantemol-N, which employs the UK Molecular R-matrix codes. These calculations were performed for the total elastic cross-sections along with their symmetrical components, differential and momentum transfer cross-sections, inelastic scattering cross-sections comprising of discrete electronic excitation, ionization and dissociative electron attachment processes. We employed the two most popular theoretical approaches to calculate the electron impact ionization cross-sections viz. Complex scattering potential-ionization contribution (CSP-ic) and the Binary encounter Bethe (BEB) model. The rate coefficients for elastic and inelastic processes were estimated over a wide electron temperature range. In addition to scattering calculations, the other motivation was to obtain resonances which are signatures of many significant low energy phenomena. The first two peak correspond to π* shape resonances which are observed at 2.1 eV and 4.69 eV and are in accordance with the earlier reported data. The third peak is observed at 10.96 eV which may be attributed to the σ* shape resonance. [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]

• 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]

• 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. 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. [ABSTRACT FROM AUTHOR]

The gas phase electronic absorption spectrum of nitrobenzene (C 6 H 5 NO 2 ) in the 4.5–11.2 eV region is recorded using synchrotron radiation with a view to comprehend the nature of the excited states. Electronic excited states of nitrobenzene are mainly classified as local excitations within the benzene ring or nitro group and charge transfer excitations between the benzene and nitro group, with some transitions showing percentage from both. The nature of molecular orbitals, their orderings and energies are obtained from density functional theory calculations which help in assigning partially assigned/unassigned features in earlier photoelectron spectroscopy studies. Optimized geometry of ionic nitrobenzene predicts redistribution of charge density in the benzene ring rather than the nitro group resulting in stabilization of the benzene ring π orbitals in comparison to the neutral molecule. Time dependent density functional theory computations are found to describe the experimental spectra well with respect to energies, relative intensities and nature of the observed transitions in terms of valence, Rydberg or charge transfer type. New insights into the interpretation of 1 B 2u ← 1 A 1g and 1 B 1u ← 1 A 1g shifted benzene transitions in light of the present computational calculations are presented. The first few members of the ns, np and nd type Rydberg series in nitrobenzene, converging to the first six ionization potentials, identified in the spectra as weak but sharp peaks are reported for the first time. In general, transitions to the lowest three unoccupied molecular orbitals 4b 1 , 3a 2 and 5b 1 are valence or charge transfer in nature, while excitations to higher orbitals are predominantly Rydberg in nature. This work presents a consolidated experimental study and theoretical interpretation of the electronic absorption spectrum of nitrobenzene. [ABSTRACT FROM AUTHOR]

• First report of absorption cross-sections of benzonitrile in the UV-VUV(4.5–11 eV). • Spectral analysis & assignment of valence, Rydberg & charge transfer transitions. • Revisit of IR spectrum & assignment of fundamental modes aided by NBO analysis. • Quantum chemical calculations using DFT & TDDFT methods to support the analysis. • PEC calculations help identify proposed hidden state as the valence state 1A2(1A"). A spectroscopic study on benzonitrile has been carried out by recording photoabsorption spectra in the 36,000–90,000 cm−1 (4.5–11 eV) region using the synchrotron light source Indus 1 and infrared spectra in the 500–4000 cm−1 region using a Fourier transform infrared spectrometer. The observed electronic spectrum encompasses rich vibrational spectra corresponding to the π→π* valence transition in the 36,000–62,000 cm−1 region. Further, the 62000–90000 cm−1 region predominantly comprises of weak Rydberg transitions of the ns and np type riding on a broad continuum. Vertical excited states calculated using the TDDFT methodology give new insights into the interpretation of the valence and Rydberg transitions by corelating them with the observed spectral peaks and shifted benzene transitions. Excited electronic states of benzonitrile are classified as local excitations and /or charge transfer excitations from the percentage contributions predicted with the aid of quantum chemical calculations. A reinvestigation of the titled compound with quantum chemical calculations using DFT methodology predict the equilibrium geometry and ground state vibrational modes, while normal coordinate analysis establishes a good agreement with the observed molecular vibrations. Theoretically generated potential energy curves of low lying excited states provide additional insights into UV spectral features, photodissociation dynamics for formation of C 5 H 5 • and CN• radicals and could establish the identity of the hidden (dark) state postulated in an earlier work. For the first time, a comprehensive study of benzonitrile in the IR and UV-VUV regions is summarized in this paper. [ABSTRACT FROM AUTHOR]