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The photoabsorption spectrum of aniline (C6H5NH2) in gas phase in the 30 000-90 000 cm-1 (3.7-11.2 eV) region is recorded at resolution limit of 0.008 eV using synchrotron radiation source for the first time to comprehend the nature of the excited valence and Rydberg states. The first half of the energy interval constitutes the richly structured valence transitions from the ground to excited states up to the first ionization potential (IP) at 8.02 eV. The spectrum in the second half consists of vibrational features up to second IP (9.12 eV) and structureless broad continuum up to the third IP (10.78 eV). The electronic states are assigned mainly to the singlets belonging to π → π* transitions. A few weak initial members of Rydberg states arising from π → 4s, np or nd transitions are also identified. Observed vibrational features are assigned to transitions from the ground state A′ to the excited states 1A″, 3A′, 5A,″ 6A′, and 10A″ in Cs symmetry. Time dependent density functional theory (TDDFT) calculations at B3LYP level of theory are employed to obtain the vertical excitation energies and the symmetries of the excited states in equilibrium configuration. The computed values of the transition energies agree fairly well with the experimental data. Further the calculated oscillator strengths are used to substantiate the assignments of the bands. The work provides a comprehensive picture of the vacuum ultraviolet photoabsorption spectrum of aniline up to its third ionization limit. [ABSTRACT FROM AUTHOR]

We report here investigations on conformational effects in the vibrational and electronic spectra of the propionaldehyde (propanal) molecule using FTIR (600–3200 cm−1) and vacuum ultraviolet (VUV) synchrotron radiation photoabsorption (52 500–85 000 cm−1) spectroscopy respectively. Detailed theoretical calculations (using DFT and TDDFT methodologies) on ground and excited states of the cis and gauche conformers of propanal are performed; a comprehensive spectral analysis of the IR and VUV spectra is presented. A reinvestigation of the IR spectrum reveals several new bands assigned to the gauche conformer based on theoretical calculations. The VUV spectrum exhibits rich Rydberg series structure assigned to ns, np and nd series converging to the first ionization potentials of the two conformers. Earlier assignments of the 3s cis and gauche origins are revised in addition to extending Rydberg series analysis to several higher members. Vibronic bands accompanying the 3s, 4s and 4p Rydberg states are assigned using estimated vibrational frequencies of cis and gauche conformers in the cationic ground state. Simulated potential energy curves of the first few excited states (singlets and triplets) of cis and gauche conformers of propanal help in gaining insights into photodissociation mechanisms and possible conformational effects therein. [ABSTRACT FROM AUTHOR]

The recent discovery of 1-propanol (CH3CH2CH2OH) in the interstellar medium (ISM) is of tremendous interest since fatty alcohols have been proposed as constituents of proto-cell membranes. Motivated by this discovery, we present the laboratory mid-infrared (MIR) and vacuum ultraviolet (VUV) absorption spectra of 1-propanol ice under astrochemical conditions, mimicking an icy mantle on cold dust in the ISM. Both MIR and VUV spectra were recorded at ultrahigh vacuum of ∼10-9 mbar and at temperatures ranging from 10 K to sublimation. The morphology of the 1-propanol ice deposited at 10 K was amorphous. By warming the ice to temperatures of 140 K and above, with subsequent recording of IR spectra, we observe complete sublimation of 1-propanol molecules from the substrate around 170 K. No amorphous-to-crystalline phase change was observed upon warming to higher temperatures. Additionally, we observe the IR and VUV signatures of 1-propanol ice on the substrate well beyond its melting point (147 K). To the best of our knowledge, this is the first reported observation of a molecular ice staying well beyond its melting point under such conditions. This result shows that the morphology of icy mantles on ISM cold dust grains is more complex than previously thought. Our atomistic molecular dynamics simulations capture the experimental trends and shed light on the microscopic origin of this unusual phase behaviour of 1-propanol. [ABSTRACT FROM AUTHOR]

We present the spectral properties of a selection of comets from both the Jupiter family and Oort cloud in the ultraviolet (UV) and mid-infrared (IR) wavelength regions. Spectroscopic measurements are retrieved from public archival data of the International Ultraviolet Explorer (IUE) and Hubble Space Observatory (HST) in the near-UV (NUV) and far-UV (FUV) wavelengths and reveal emissions from Polycyclic Aromatic Hydrocarbon (PAH) molecules, such as pentacene (C 22 H 14 ) at 1902, 2795 Å and toluene (C 7 H 8 ) at 2681 Å. UV spectra of the comets also show emissions due to CS, Fe II, CO Cameron bands, C I, S I and O I. Mid-IR spectroscopic observations made using the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope for a few comets reveal the presence of PAH bands at 6.2, 7.7, 8.6, 11.2 μ m. Mid-IR spectra of the comets also reveal the presence of silicate at 9.7 μ m. The similarity of PAH signatures observed in the proto-planetary disks of young stellar objects, meteorites, interplanetary dust particles and comets with those observed in the interstellar medium (ISM) suggests a possible scenario for the incorporation of PAH from ISM into the primordial solar nebula. [ABSTRACT FROM AUTHOR]

The recent identification of the polycyclic aromatic hydrocarbon molecules, 1-cyanonaphthalene, and 2-cyanonaphthalene in the interstellar medium (ISM) requires laboratory support to understand the physicochemical nature of these molecules when they are present as icy mantles on cold dust grains. Therefore, we have carried out the infrared spectroscopic characterization of these molecules under astrochemical conditions. When deposited at 7 K, the spectra of the cyanonaphthalene ices were amorphous in nature. Upon warming to higher temperatures, cyanonaphthalene ices appear to remain amorphous until sublimation. Both sublimate at very high temperatures, 250-265 K, suggesting their presence on the ISM dust over a large temperature range such that they may influence the chemical complexity across the ISM. SYNOPSIS Infrared spectroscopic characterization of cyanonaphthalene molecules under astrochemical conditions were carried. Cyanonaphthalene ices show no phase change upon warming. Cyanonaphthalene sublimation at very high temperatures, 250-265 K, suggests their presence on the ISM dust over a large temperature range and may further influence the chemical complexity. [ABSTRACT FROM AUTHOR]

In our quest for the presence of large complex molecules containing a majority of carbon in the interstellar medium (ISM), the search for graphene plays a central role due to its nature in making other carbon structures. Although the ingredients for graphene synthesis are present in the ISM, conclusive laboratory evidence of such formation is lacking. Therefore, in our laboratory experiments simulating the cold ISM conditions, we subjected icy mantles of benzonitrile, an aromatic with a cyanide side chain that has recently been detected in the interstellar medium, to vacuum ultraviolet photon irradiation. The irradiated ice was observed to leave a residue upon warming to room temperature. The residue was removed from the substrate and placed on a Quantifoil grid for electron microscopy analysis. Transmission electron microscopy showed quantum dots (QD) and nitrogen-doped graphene (N-Graphene) sheets. Diffraction and energy-dispersive X-ray spectroscopy revealed the crystalline nature and carbon–nitrogen composition, of the observed graphene sheet. This is the first evidence of QD and N-graphene synthesis in ice irradiation at interstellar temperatures. [ABSTRACT FROM AUTHOR]

The fate of organometallic dust subjected to extreme conditions, especially the shock fronts, in the interstellar medium (ISM) has not been explored to date. Iron and cyclopentadiene, which have been found to be present in the ISM, are known to react and produce the organometallic compound ferrocene under terrestrial conditions. In our experiment we subjected ferrocene, a possible proxy of such dust, to ∼5.6 Mach (M) shock commensurate with conditions encountered in the ISM, leading to a temperature rise up to 7300 K within 2 ms. Analysis of the post-shock residue showed the presence of a α-Fe and Fe3C composite that responded to an external magnetic field. These results show that a non-magnetic dust composed of molecules containing transition metals undergoing shock processing in the ISM can dissociate and synthesize dust that is then magnetic. Such drastic transformations from non-magnetic to magnetic dust induced by shocks might be of importance in interstellar polarization. [ABSTRACT FROM AUTHOR]

The recent discovery of hydroxylamine (NH2OH) molecule in the interstellar medium emphasizes the need to study the molecule in laboratory astrochemical ice analogues. Here, we present the first vacuum ultraviolet photoabsorption spectrum of hydroxylamine ice synthesized in-situ in an ammonia–oxygen (6:1) ice mixture irradiated by ~ 10 eV photons from synchrotron radiation source. The appearance of a new band between the 180–240 nm, with a band centered at ~ 207 nm, is assigned to the characteristic absorption of hydroxylamine molecule in the ice phase. This band maybe used in ammonia dominated, oxygen bearing, icy surfaces for the identification of hydroxylamine. [ABSTRACT FROM AUTHOR]