Exploring new molecular species on the (1)[H, Se, F] singlet potential energy surface: Energetics, structures, IR spectra, and heats of formation

Structural, energetic, and vibrational properties of new molecular species, HSeF and HFSe, the associated transition state, and dissociation fragments are investigated using a state-of-the-art theoretical approach, CCSD(T)/CBS. HSeF is a normal covalently bonded molecule 38.98 kcal mol (1) more stable than the complex HF-Se, which shows an unusual structure with a central fluorine atom and a bond angle of 101.8 degrees.A barrier (Delta G(#)) of 49.01 kcal mol (1) separates the two species. Vibrational frequencies are also quite distinct. Heats of formation are evaluated for the diatomic fragments and HSeF. Final Delta(f)H values depend on the experimental accuracy of those of Se(g) and H(2)Se. (c) 2009 Elsevier B.V. All rights reserved.

Electronic structure and spectra of a new molecular species: SI. A theoretical contribution

A high level theoretical approach is used to characterize for the first time a manifold of doublet and quartet A + S and Omega states correlating with the first two dissociation channels of an as yet experimentally unknown molecular species, SI, sulfur monoidide. A set of spectroscopic constants is determined, including vibrationally averaged spin-orbit coupling constants, vibrationally averaged dipole moments, and dissociation energies. The transition dipole moment function for the spin-forbidden transition a (4)Sigma -X (2)Pi, and the associated radiative lifetimes were also evaluated. Two possibilities to detect transitions experimentally and to derive spectroscopic constants are suggested. (C) 2011 Elsevier B. V. All rights reserved.

Studies on the resonance Raman spectra of polyaniline obtained with near-IR excitation

The effects of near-IR (NIR) laser power over the Raman spectra of poly(aniline) emeraldine salt (PANIES) and base (PANI-EB) were investigated. The reasons for the existence of several bands from 1324 to 1500 cm-1 in the Raman spectra of poly(aniline) obtained at NIR region were also studied. The bands from 1324 to 1375 cm-` were associated to vC-N of polarons with different conjugation lengths and the bands from 1450 to 1500 cm-1 in Raman spectra of PANI emeraldine and pernigraniline base forms were correlated to vC=N modes associated with quinoid units having different conjugation lengths. The increase of laser power at 1064.0 run causes the deprotonation of PANI-ES and the formation of cross-linking segments having phenazine and/or oxazine rings. For PANI-EB only a small spectral change is observed when the laser power is increased, owing to the low absorption of this form in the NIR region. Copyright (c) 2007 John Wiley & Sons, Ltd.

Understanding the Effect of Adsorption Geometry over Substrate Selectivity in the Surface-Enhanced Raman Scattering Spectra of Simazine and Atrazine

This paper studies the selectivity of Well-defined Au and Ag nanostructures as substrates for the SERS, (surface-enhanced Raman scattering) detection of simazine (6-chloro-N,N`-diethyl-1,3,5-triazine-2,4-diamine) and atrazine (6-chloro-N-ethyl-N`-isopropyl-1,3,5-triazine-2,4-diamine). Our data showed that simazine and atrazine displayed similar SERS spectra when the Au was employed as substrate. Conversely, distinct SERS signatures were obtained upon the utilization of Ag substrates. Density functional theory (DFT) calculations and vibrational assignments suggested that, while simazine and atrazine adsorbed on Au via the N3 position of the triazine ring, simazine adsorbed on Ag via N3 and atrazine via N5. The results presented herein demonstrated that the adsorption geometry of analyte molecules can play a central role over substrate selectivity in SERS, which is particularly important in applications involving ultrasensitive analysis of mixtures containing structurally similar molecules.

Raman spectra of acetonitrile in imidazolium ionic liquids

Raman spectra of dilute solutions of acetonitrile in ionic liquids reveal the characteristic features of ionic liquids` polarity. This is accomplished by investigating the Raman bandshape of the nu (CN) band, corresponding to the CN stretching mode of CH(3)CN, which is a very sensitive probe of the local environment. The amphiphilic nature of the CH(3)CN molecule allows us to observe the effect of electron pair acceptor and electron pair donor characteristics on ionic liquids. It has been found that the overall polarity of nine different ionic liquids based on 1-alkyl-3-methylimidazolium cations is more dependent on the anion than cation. The observed wavenumber shift of the nu (CN) band of CH(3)CN in ionic liquids containing alkylsulfate anions agrees with the significant different values previously measured for the dielectric constant of these ionic liquids. The conclusions obtained from the analysis of the nu (CN) band were corroborated by the analysis of the symmetric nu(1) (CD(3)) stretching mode of deuterated acetonitrile in different ionic liquids. Copyright (C) 2010 John Wiley & Sons, Ltd.

Raman spectra of polymer electrolytes based on poly(ethylene glycol) dimethyl ether, lithium perchlorate, and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate

Raman spectra of polymer electrolytes based on poly(ethylene glycol) dimethyl ether (PEGdME) with LiClO(4), PEGdME/LiClO(4), and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, PEGdME/[bmim]PF(6), are compared. Raman spectroscopy suggests stronger interactions in PEGdME/LiClO(4) than PEGdmE/[bmim]PF(6), thus corroborating previous results obtained by molecular dynamics simulations. Quantum Chemistry methods have been used to calculate vibrational frequencies and the equilibrium structure of segments of the polymer chain around the cation. A consistent picture has been obtained from Raman spectroscopy, density functional theory (DFT) calculations, and molecular dynamics simulations for these polymer electrolytes. (C) 2010 Elsevier B.V. All rights reserved.

Complete assignment of (1)H and (13)C NMR spectra of alpha-phenylsulfinyl-N-methoxy-N-methylpropionamide and some p-substituted derivatives

The complete assignment of the (1)H and (13)C NMR spectra of the diastereomeric pairs of some alpha-arylsulfinyl-substituted N-methoxy-N-methylpropionamides with the substituents methoxy, methyl, chloro, nitro is reported. Copyright (C) 2008 John Wiley & Sons, Ltd.

Fast Acquisition of (13)C NMR Spectra using the Steady-state Free Precession Sequence

In this paper, we show that the steady-state free precession sequence can be used to acquire (13)C high-resolution nuclear magnetic resonance spectra and applied to qualitative analysis. The analysis of brucine sample using this sequence with 60 degrees flip angle and time interval between pulses equal to 300 ms (acquisition time, 299.7 ms; recycle delay, 300 ms) resulted in spectrum with twofold enhancement in signal-to-noise ratio, when compared to standard (13)C sequence. This gain was better when a much shorter time interval between pulses (100 ms) was applied. The result obtained was more than fivefold enhancement in signal-to-noise ratio, equivalent to more than 20-fold reduction in total data recording time. However, this short time interval between pulses produces a spectrum with severe phase and truncation anomalies. We demonstrated that these anomalies can be minimized by applying an appropriate apodization function and plotting the spectrum in the magnitude mode.