The gas-phase infrared spectra of anthracene-h10 and anthracene-d10

Photochemistry of coronene in cosmic water ice analogs at different concentrations

This work presents the photochemistry of ultraviolet (UV) irradiated coronene in water ices at 15 K, studied using mid-infrared Fourier transform (FTIR) spectroscopy for C24H12:H2O at concentrations of (1:50), (1:150), (1:200), (1:300) and (1:400). Previous UV irradiation studies of anthracene:H2O, pyrene:H2O and benzo[ghi]perylene:H2O ices at 15 K have shown that aromatic alcohols and ketones, as well as CO2 and H2CO are formed at very low temperatures. Like-wise, here, in addition to the coronene cation, hydroxy-, keto-, and protonated coronene (coronene-H+) are formed. The rate constants for the decay of neutral coronene and for the formation of photoproducts have been derived. It is shown that PAHs and their UV-induced PAH:H2O photoproducts have mid-infrared spectroscopic signatures in the 5-8 μm region that can contribute to the interstellar ice components described by Boogert et al. (2008) as C1-C5. Our results suggest that oxygenated and hydrogenated PAHs could be in UV-irradiated regions of the ISM where water-rich ices are important.

The far-infrared spectrum of azulene and isoquinoline and supporting anharmonic density functional theory calculations to high resolution spectroscopy of polycyclic aromatic hydrocarbons and derivatives

In the laboratory, the acquisition and analysis of the rotationally resolved spectra of large molecular systems remain challenging. We report in this paper the rotational analysis of the ν30-GS band of azulene and the ν41-GS band of isoquinoline recorded with synchrotron-based Fourier transform absorption spectroscopy in the far-IR. As a support to rotational analyses, we employed a method based on standard density functional theory calculations performed at the anharmonic level which accurately reproduced the rotational constants of 28 vibrational states of 16 Polycyclic Aromatic Hydrocarbons (PAHs) and aza-derivatives. This method appears as an invaluable support for the spectral assignment of the very congested rotational structures of the infrared bands of PAH species and should be very helpful in the active search of these molecules in space through their pure rotational or rovibrational spectra.

Vibrational spectroscopic studies and molecular docking of 10,10-Dimethylanthrone

FT-IR and FT-Raman spectra of 10,10-Dimethylanthrone were recorded and analyzed. The vibrational wavenumbers were computed using DFT quantum chemical calculations. The data obtained from wavenumber calculations are used to assign vibrational bands obtained experimentally. In its most stable form, the title compound maintains C2v symmetry as determined by XRD results, where both methyl groups are staggered with respect to the corresponding C23-C24 and C23-C28 bonds. The geometrical parameters (B3LYP/6-311++G(d,p)(5D,7F)) of the title compound are in agreement with the XRD results. The calculated HOMO and LUMO energies allow the calculations of atomic and molecular properties and they also showed that charge transfer occurs in the molecule. A detailed molecular picture of the title compound and its interactions were obtained from NBO analysis. As seen from the MEP map, negative potential regions are localized over the carbonyl group and are possible sites for electrophilic attack. The title compound, 10,10-Dimethylanthrone forms a stable complex with human topoisomerase-II as is evident from the ligand-receptor interactions and show appreciable antineoplastic activity.

Formation of nitroanthracene and anthraquinone from the heterogeneous reaction between NO2 and anthracene adsorbed on NaCl particles

Oxidative derivatives of polycyclic aromatic hydrocarbons (PAHs), that is, nitro-PAHs and quinones, are classed as hazardous semivolatile organic compounds but their formation mechanism from the heterogeneous reactions of PAHs adsorbed on atmospheric particles is not well understood. The heterogeneous reaction of NO2 with anthracene adsorbed on NaCl particles under different relative humidity (RH 0-60%) was investigated under dark conditions at 298 K. The formation of the major products, 9,10-anthraquinone (9,10-AQ) and 9-nitroanthracene (9-NANT), were determined to be second-order reactions with respect to NO2 concentration. The rate of formation of 9,10-AQ under low RH (0-20%) increased as the RH increased but decreased when the RH was further increased in high RH (40-60%). In contrast, the rate of formation of 9-NANT across the whole RH range (0-60%) decreased significantly with increasing RH. Two different reaction pathways are discussed for the formation of 9,10-AQ and 9-NANT, respectively, and both are considered to be coupled to the predominant reaction of NO2 with the NaCl substrate. These results suggest that relative humidity, which controls the amount of surface adsorbed water on NaCl particles, plays an important role in the heterogeneous reaction of NO2 with adsorbed PAHs.

Vibrational spectroscopic (FT-IR, FT-Raman, SERS) and quantum chemical calculations of 3-(10,10-dimethyl-anthracen-9-ylidene)-N,N,N-trimethylpropanaminiium chloride (Melitracenium chloride)

FT-IR, FT-Raman spectra of Melitracenium chloride were recorded and analyzed. SERS spectrum was recorded in silver colloid. The vibrational wavenumbers were computed using DFT quantum chemical calculations. The data obtained from wavenumber calculations are used to assign vibrational bands obtained in infrared and Raman spectra as well as in SERS of the studied molecule. Potential energy distribution was done using GAR2PED program. The geometrical parameters (SDD) of the title compound are in agreement with the XRD results. The presence anthracene ring modes in the SERS spectrum suggest a tilted orientation with respect to the metal surface. The methyl groups in the title molecule are also close to the metal surface. The first hyperpolarizability, NBO analysis and molecular electrostatic potential results are also reported.

Infrared spectra of dimethylphenanthrenes in the gas phase

Infrared spectra of atmospherically and astronomically important dimethylphenanthrenes (DMPs), namely 1,9-DMP, 2,4-DMP, and 3,9-DMP, were recorded in the gas phase from 400 to 4000 cm(-1) with a resolution of 0.5 cm(-1) at 110 °C using a 7.2 m gas cell. DFT calculations at the B3LYP/6-311G** level were carried out to get the harmonic and anharmonic frequencies and their corresponding intensities for the assignment of the observed bands. However, spectral assignments could not be made unambiguously using anharmonic or selectively scaled harmonic frequencies. Therefore, the scaled quantum mechanical (SQM) force field analysis method was adopted to achieve more accurate assignments. In this method force fields instead of frequencies were scaled. The cartesian force field matrix obtained from the gaussian calculations was converted to a nonredundant local coordinate force field matrix and then the force fields were scaled to match experimental frequencies in a consistent manner using a modified version of the UMAT program of the QCPE package. Potential energy distributions (PEDs) of the normal modes in terms of nonredundant local coordinates obtained from these calculations helped us derive the nature of the vibration at each frequency. The intensity of observed bands in the experimental spectra was calculated using estimated vapor pressures of the DMPs. An error analysis of the mean deviation between experimental and calculated intensities reveal that the observed methyl C-H stretching intensity deviates more compared to the aromatic C-H and non C-H stretching bands.

IR and Raman spectra of nitroanthracene isomers: substitional effects based on density functional theory study

Structure, IR and Raman spectra of 1-, 2- and 9-nitroanthracene isomers (1-NA, 2-NA and 9-NA) were calculated and analyzed through density functional theory computations using the B3LYP functional with the 6-311+G** basis set. Steric and π-conjugative effects determine the characteristic ONCC dihedral angles, which vary from 0° (2-NA) to 28-29° (1-NA) and 59° (9-NA), influencing the relative order of stability along the series 9-NA<1-NA<2-NA. The spectral regions at wavenumber values>3000 cm(-1) and <1000 cm(-1) little depend on the substituent position. The Raman and IR intensity values of the characteristic symmetric nitro group stretching transition, appearing between 1310 and 1345 cm(-1), are rather sensitive to the position of the substituent, decreasing regularly on passing from the planar to the NO2-rotated isomers (9-NA<1-NA<2-NA). In the medium-energy spectral region (1000-1700 cm(-1)), the number and the relative position of the strongest Raman bands are of potential utility to discriminate the NA isomers. Structural and spectroscopic results suggest that the unknown mutagenic activity of 1-NA is expected to be between that of 9-NA and 2-NA.

FT-IR, FT-Raman spectroscopy and computational study of (E)-4-((anthracen-9-ylmethylene)amino)-N-carbamimidoylbenzene sulfonamide

The infrared and Raman spectra of (E)-4-((anthracen-9-ylmethylene)amino)-N-carbamimidoylbenzene sulfonamide have been recorded and analysed. Geometry and harmonic vibrational wavenumbers were calculated theoretically using Gaussian03 set of quantum chemistry codes. The data obtained from vibrational wavenumber calculations are used to assign vibrational bands found in infrared and Raman spectra of the studied molecule. The red-shift of the NH stretching band in the infrared spectrum from the computed wavenumber indicates the weakening of the NH bond. The NH stretching band has split into a doublet in the IR spectrum owing to the Davydov coupling between neighbouring units. The geometrical parameters of the title compound are in agreement with the reported similar derivatives. The calculated first hyperpolarizability is comparable with the reported value of similar structures and may be an attractive object for further studies on non-linear optics. The important thermodynamical parameters are also reported.

Far-infrared spectroscopy of small polycyclic aromatic hydrocarbons

Both experimental and theoretical spectroscopic studies on small gas phase polycyclic aromatic hydrocarbons in the far-infrared spectral region are reported. The experimental set-up based on thermal emission and Fourier transform far infrared analysis led to the detection of relatively broad vibrational bands, unresolved in rotation, representative of each molecule. Detailed theoretical investigations were performed, including both ab initio calculations and spectral simulations. For the majority of the samples, this study provides the first detection of the vibrational modes associated with the skeleton motions.

Structural and Vibrational Properties of Tetraoxaporphyrin Dication, the Oxygen Analogue of Porphyrin, and of Isoelectronic Diprotonated Porphyrin

Structural calculations by means of the density functional method have been performed on tetraoxaporphyrin dication and on isoelectronic diprotonated porphyrin as well as on the sulfur and carbon analogues of porphyrin. A detailed study of the stable conformations of these compounds is reported starting with the most symmetrical conformations and lowering the symmetry along the vibrational coordinates with imaginary frequency. The calculated geometries are related to experimental structures available from X-ray diffraction studies. The Raman spectra of tetraoxaporphyrin dication exciting with micro-Raman instrumentation at 785 nm and of diprotonated porphyrin in near-resonance conditions with the Soret band have been measured. The correlation between frequencies calculated with the DF/B3-LYP/cc-pVDZ procedure for porphyrin, diprotonated porphyrin, and tetraoxaporphyrin dication has allowed for making a vibrational assignment for the latter two systems in excellent agreement with experiment using a single frequency scale factor.