Far infrared spectrum of orthorhombic sulphur

Absorption spectra in the region 10 - 170 cm^?1 of polycrystalline samples of orthorhombic sulphur have been recorded at 300K and 4.2 K. 5 lattice peaks and the multiplets of the v₈ and v₉ internal modes have been observed. Comparisons with results from recent Raman and neutron scattering experiments and with group theoretical and lattice dynamics calculations give very satisfactory agreement.     

Theoretical modeling of the O-H stretching IR bands of hydrogen-bonded dimers of benzoic acid in S(0) and S(1) electronic states

Theoretical model for vibrational interactions in the hydrogen-bonded dimer of benzoic acid is presented. The model takes into account anharmonic-type couplings between the high-frequency O-H and the low-frequency O[cdots, three dots, centered]O stretching vibrations in two hydrogen bonds, resonance interactions (Davydov coupling) between two hydrogen bonds in the dimer, and Fermi resonance between the O-H stretching fundamental and the first overtone of the O-H in-plane bending vibrations. The vibrational Hamiltonians and selection rules for the C(2h) geometry in the S(0) state and for the C(s) in-plane bent geometry in the S(1) state of the dimer are derived. The model is used for theoretical simulation of the O-H stretching IR absorption bands of benzoic acid dimers in the gas phase in the electronic ground and first excited singlet states. Ab initio CIS and CIS(D)6-311++G(d,p) calculations have been performed to determine geometry, frequencies, and excited state energies of benzoic acid dimer in the S(1) state.     

Geometrical,electrical, and energetic parameters of hetero-disubstituted cumulenes and polyynes in the presence and absence of the external electric field

Structural Chemistry - Cumulenes and polyynes have the potential to be applied as linear, sp-hybridized, one-dimensional all-carbon nanowires in molecular electronics and optoelectronics. The...     

Monodentate coordinated chromate(VI) ion in [Cu(phen)<Subscript>2</Subscript>OCrO<Subscript>3</Subscript>](phen)<Subscript>0.5</Subscript>·4H<Subscript>2</Subscript>O completing the square pyramidal geometry of the copper(II) in the solid state

Novel copper(II) complex of the formula [Cu(phen)₂OCrO₃](phen)_0.5 ·4H₂O (1) (phen = 1,10-phenantroline) was prepared in the crystalline form and characterized by X-ray diffraction and spectroscopic methods (IR-FIR, NIR-Vis–UV, EPR). In the solid state, the CuN₄O chromophore adopts a slightly distorted square-pyramidal geometry around the Cu²⁺ ion with a magnitude of a distortion parameter τ = 0.14. The chromate unit in (1) was found to be a monodentate.     

Theoretical modeling of infrared spectra of hydrogen-bonded crystals of salicylic acid

A theoretical model for the infrared spectra in the O-H stretching region of hydrogen-bonded salicylic acid is presented. Based on the model, infrared spectrum in the O-H stretching region is calculated for salicylic acid and compared with the experimental one. The experimental and theoretical spectra are in good agreement.     

Picosecond time-evolution of the fluorescence spectrum of a large aromatic hydrocarbon molecule in solution at 300K

A new Nd³⁺-YAG laser configuration has been used to obtain fluorescence spectra of a large aromatic molecule with about 12 ps time-resolution. The data presented are both in the form of time-profiles at selected wavelengths and more importantly fluorescence spectra recorded at 6.7 ps intervals around the irradiation event. The sample molecule was 3,4,9,10-dibenzpyrene in hexane at 300 K. The major result was the observation of two short-lived transients in the region 380–480 nm characterized by rather diffuse spectra. One, which included a strong “hot-band”, was clearly pulse- limited and is assigned to the second excited singlet state. The second transient was considerably weaker and survived beyond the irradiation pulse. This had characteristics of a vibrational quasicontinuum in the S₁ state. Out of these evolved the familiar structured spectrum characteristic of thermalised S₁ → S₀ fluorescence. In a related experiment, the ultraviolet fluorescence spectrum (230–340 nm) of two-photon-excited higher states of the same molecule was shown to depend on the time-delay between two excitation pulses.     

Theoretical and spectroscopic study of infrared spectra of hydrogen-bonded 1-methyluracil crystal and its deuterated derivative

Theoretical simulation of the band shape and fine structure of the N-H(D) stretching band is presented for 1-methyluracil and its deuterated derivative taking into account anharmonic coupling between the high-frequency N-H(D) stretching and the low-frequency N...O stretching vibrations, resonance interaction between two equivalent hydrogen bonds in the dimer, anharmonicity of the potentials for the low-frequency vibrations in the ground and excited state of the N-H(D) stretching mode, Fermi resonance between the N-H(D) stretching and the first overtone of the N-H(D) bending vibrations, and electrical anharmonicity. The effect of deuteration has been successfully reproduced by our model calculations. Infrared, far-infrared, Raman, and low-frequency Raman spectra of the polycrystalline 1-methyluracil have been recorded. The geometry and experimental frequencies are compared with the results of harmonic and anharmonic B3LYP6-311++G(**) calculations.     

Spectroscopic and theoretical study of vibrational spectra of hydrogen‐bonded tropolone

Theoretical simulation of the bandshape and fine structure of the ν_s stretching band is presented for tropolone‐H and tropolone‐D taking into account an adiabatic coupling between the high‐frequency O–H(D) stretching and the low‐frequency intra‐ and intermolecular OO stretching modes, and linear and quadratic distortions of the potential energies for the low‐frequency vibrations in the excited state of the O–H(D) stretching vibration. In order to determine the low‐frequency vibrations, the experimental spectra of the polycrystalline tropolone in the far‐infrared and the low‐frequency Raman range have been recorded for the first time. The experimental frequencies in the low‐frequency region are compared with the results of the HF/6‐31G** and Becke3LYP/6‐31G** calculations carried out for the tropolone dimer. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 73: 275–282, 1999     

Theoretical modeling of infrared spectra of benzoic acid and its deuterated derivative

Theoretical simulation of the ν_s stretching band is presented for benzoic acid and its OD derivative at 300 K. The simulation takes into account an adiabatic coupling between the high-frequency O–H(D) stretching and the low-frequency intermolecular OO stretching modes, linear and quadratic distortions of the potential energy for the low-frequency vibrations in the excited state of the O–H(D) stretching vibration, resonance interaction between the two hydrogen bonds in the dimer, and Fermi resonance between the fundamental ν OH(D) stretching and the overtone of the δ O–H(D) bending vibrations.

Infrared, far-infarared, Raman and low-frequency Raman spectra of the polycrystalline benzoic acid and its deuterated form have been measured. The geometry and experimental frequencies are compared with the results of our B3LYP/6-311++G** and B3LYP/cc-pVTZ calculations.