Computer simulation of the adsorption of acetylene by disperse aqueous medium. IR spectra

Adsorption of acetylene molecules by water clusters at T 230 K was studied by the method of molecular dynamics. Addition of already two C₂H₂ molecules to (H₂O) _n clusters (10 ≤ n ≤ 20) makes them thermodynamically unstable. With an increase in the acetylene concentration in the disperse aqueous system, the IR absorption by the cluster system in the frequency range 0 ≤ ω ≤ 1000 cm^?1 increases. Depending on the number of C₂H₂ molecules per water cluster, the IR reflection by cluster systems can either increase or decrease. The power of the thermal radiation emitted by the clusters considerably increases after the adsorption of C₂H₂ molecules and grows with an increase in the acetylene concentration in the disperse aqueous system.     

IR spectra of water clusters with captured ethane molecules: Computer simulation

Uptake of ethane molecules by a monodisperse aqueous system was simulated by molecular dynamics. The cluster (H₂O)₂₀ characterizing the system remains stable until the number of the captured C₂H₆ molecules becomes larger than four. Addition of ethane molecules to the disperse aqueous system decreases both the real and imaginary parts of the dielectric permittivity in the frequency range 0 ≤ ω ≤ 1000 cm^?1. The integral IR absorption coefficient of the disperse system containing C₂H₆ molecules increases, and the frequency-average reflection coefficient decreases. The continuous reflection spectra transform into band spectra. The heat-radiating power of the clusters decreases upon absorption of ethane molecules. The cluster that took up two ethane molecules exhibits the highest radiating power. This cluster has the largest number of active electrons interacting with the arriving wave.     

Computer-aided study of oxygen absorption by water clusters. IR spectra of heteroclusters

Spectral characteristics of (H₂O)_n, (O₂)_m(H₂O)_n, and (O)_i(H₂O)_n cluster systems, where m≤2, i≤4, and 10 ≤ n ≤ 50, are studied with the molecular dynamics method using a flexible molecule model. The IR absorption spectra are changed substantially as a result of O₂ molecule dissociation, and in the presence of atomic oxygen in the clusters, the spectra are characterized by a deep minimum at 520 cm^?1. The absorption of oxygen causes a marked reduction in reflection coefficient R of monochromatic IR radiation. The number of peaks in the R(ω) spectra decreases to two in the case of molecular oxygen absorption and is no larger than four in the case of atomic oxygen absorption. The absorption of atomic oxygen by the clusters is also accompanied by a significant increase in the dissipation of energy accumulated by the clusters. This effect weakens when molecular oxygen is absorbed. An increase in atomic oxygen concentration in the clusters renders their radiation harder.     

IR absorption and Raman spectra of silicon dioxide nanoparticles in the presence of water: Computer experiment

Interactions of (SiO₂)₅₀ clusters with 10, 20, 30, or 40 water molecules are studied by molecular dynamics method. Flat SiO₂ nanoparticle covered with a water layer is formed after the inclusion of water molecules into the cluster. As a rule, the integral intensity of IR and Raman spectra lowers after the absorption of H₂O molecules by the cluster. The power of IR radiation emitted by the cluster increases nonmonotonically with the addition of water molecules to the cluster. The absorption of water molecules by the cluster leads to a significant increase in the absorption coefficient and only a slight increase in the refractive index. The number of electrons participating in the interaction with electromagnetic radiation increases with the addition of water molecules to the cluster.     

IR absorption,reflection, and emission spectra of aqueous disperse systems interacting with nitric oxide

IR absorption, reflection, and emission spectra of aqueous disperse systems that absorbed molecules of nitric oxide are calculated. In order to reveal the effect of the absorption of NO molecules on the dielectric properties of water clusters with different sizes, clusters are divided into two groups. The first group consists of clusters containing two to ten water molecules, while the second group contains from 11 to 20 H₂O molecules. Six systems of clusters are studied, e.g., (H₂O) _n , and (NO)₂(H₂O) _n with 2 ≤ n ≤ 10 and 11 ≤ n ≤ 20 ranges. An increase in the cluster size in each group leads to the amplification of absorption, reflection, and the power of emission of IR radiation. The doubling of the NO concentration in the disperse system results in weak changes in the absorption of IR radiation, reduces the reflection and decreases the number of electrons participating in the interaction with external IR radiation, as well as significantly lowers the power of thermal radiation emitted by the system.     

IR absorption spectra of 1-aryl-3-pyrazolidones

An examination of the frequencies and intensities of the valence vibration bands of carbonyl groups established that the phenyl group interacts with the C=O group of 1-phenyl-3-pyrazolidone and its m- and p-tolyl derivatives in solution. It is assumed that the interaction is accomplished through the N₁ and N₂ atoms in the sp² state. 1-Phenylpyrazolidone derivatives are strongly associated in CC1₄ and CHCl₃ solutions. The association decreases on passing from CCl₄ to CHCl₃ solutions and when there are methyl groups in the ortho positions of the phenyl rings. The energy of association between the 1-phenylpyrazolidones and organic bases (acetonitrile, ethyl acetate, and dioxane), evaluated from the shift in _nh, is 1.36–3.5 kcal/mole. The frequencies and integral intensities of the bands of the C=O and NH groups in chloroform were measured.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1678–1682, December, 1970.     

IR absorption spectra of some aminoalcohols in the gas phase

The IR spectra of aminoalcohols in the gas phase show that in practically all instances (with the exception of N-allylaminoethanol) they are present mainly as monomers, with or without intramolecular H-bonds (IHB), the former predominating in the vicinal compounds. In 1,4-aminoalcohols the concentrations of molecules with and without IHB are practically equalized. The strongest IHB occur in the seven-membered intramolecular rings which are formed in 4-aminobutan-1-o1, for which the greatest difference is observed between the frequencies of the free OH groups and those bound in IHB. Analysis of the effect of an increase in temperature on the intensities of the OH bands of the free OH groups and of those bound in IHB shows that the partial rupture of the IHB occurs to a greater extent in the unsubstituted aminoalcohols of the vicinal series than in aminoalcohols with two alkyl substituents on the amino group. The IHB exhibit less tendency to break with rise in temperature in the vicinal aminoalcohols than in the 1,3- and 1,4-aminoalcohols.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1323–1333, June, 1990.     

Quantum-chemical calculations of the IR absorption spectra of modified polytetrafluoroethylene forms

DFT(B3LYP) (basis set 6–31 + G(d)) and HF (basis set 6–31G) calculations were performed to determine the geometric structure and vibrational spectra of the C_nF_2n and C_nF_2n O molecules (n = 3–13). The IR spectra of chain C_nF_2n O molecules with the terminal carbonyl group (-COF) were found to contain a band at 1885 cm^?1. The C=C and C=O stretching vibrations of the-CF=CF₂ and COF terminal groups were independent, and there was no mutual influence of their frequencies starting with the seven-fragment molecule. In the presence of chain branching, the sensitivity of the ν(C=C) and ν(C=O) frequencies in the olefin and carbonyl groups depended on where branching occurred. The chain configuration was found to be energetically favorable compared with branched structures.     

Isomers of HSCO: IR absorption spectra of t-HSCO in solid Ar

Irradiation of an Ar matrix sample containing H2S and CO (or OCS) with an ArF excimer laser at 193 nm yields trans-HSCO (denoted t-HSCO). New lines at 1823.3, 931.6, and 553.3 cm(-1) appear after photolysis and their intensity enhances after annealing; secondary photolysis at 248 nm diminishes these lines and produces OCS and CO. These lines are assigned to C-O stretching, HSC-bending, and C-S stretching modes of t-HSCO, respectively, based on results of 13C-isotopic experiments and theoretical calculations. Theoretical calculations using density-functional theories (B3LYP and PW91PW91) predict four stable isomers of HSCO: t-HSCO, c-HSCO, HC(O)S, and c-HOCS, listed in increasing order of energy. According to calculations with B3LYP/aug-cc-pVTZ, t-HSCO is planar, with bond lengths of 1.34 A (H-S), 1.81 A (S-C), and 1.17 A (C-O), and angles angle HSC congruent with 93.4 degrees and angle SCO congruent with 128.3 degrees; it is more stable than c-HSCO and HC(O)S by approximately 9 kJ mol(-1) and more stable than c-HOCS by approximately 65 kJ mol(-1). Calculated vibrational wave numbers, IR intensities, and 13C-isotopic shifts for t-HSCO fit satisfactorily with experimental results. This new spectral identification of t-HSCO provides information for future investigations of its roles in atmospheric chemistry.     

pH-dependent x-ray absorption spectra of aqueous boron oxides

Near edge x-ray absorption fine structure (NEXAFS) spectra at the boron K-edge were measured for aqueous boric acid, borate, and polyborate ions, using liquid microjet technology, and compared with simulated spectra calculated from first principles density functional theory in the excited electron and core hole (XCH) approximation. Thermal motion in both hydrated and isolated molecules was incorporated into the calculations by sampling trajectories from quantum mechanics∕molecular mechanics simulations at the experimental temperature. The boron oxide molecules exhibit little spectral change upon hydration, relative to mineral samples. Simulations reveal that water is arranged nearly isotropically around boric acid and sodium borate, but the calculations also indicate that the boron K-edge NEXAFS spectra are insensitive to hydrogen bonding, molecular environment, or salt interactions.     

Theoretical study of absorption and fluorescence spectra of firefly luciferin in aqueous solutions

The absorption and fluorescence spectra of firefly luciferin, which is an analog of oxyluciferin, are investigated by performing the density functional theory (DFT) calculations, especially focusing on the experimentally unassigned peaks. Time-dependent DFT calculations are performed for the excited states of firefly luciferin and its conjugate acids and bases. We find that (1) the peaks in the experimental absorption spectra correspond to the excited states of not only (6'O(-), 4COO(-)) and (6'OH, 4COO(-)), but also (6'OH, 4COOH) and (6'OH, 3H(+), 4COOH); (2) the peaks in the experimental fluorescence spectra correspond to the excited states of not only (6'O(-), 4COO(-)), but also (6'OH, 4COO(-)), (6'O(-), 4COOH), (6'OH, 4COOH) and (6'OH, 3H(+), 4COOH); (3) the unassigned peak near 400 nm in the experimental absorption spectra at pH 1 is assigned to the absorption from the equilibrium ground state to the first excited state of (6'OH, 3H(+), 4COOH); and (4) the unassigned peak at 610 nm in the experimental fluorescence spectra corresponds to the transition from the equilibrium first excited state to the ground state of (6'OH, 4COO(-)).     

IR spectra of aqueous disperse systems adsorbing atmospheric gases: 2. Argon

The absorption, reflection, and scattering of IR radiation by aqueous ultradisperse systems that absorb argon are studied with the molecular dynamics method on the basis of a flexible molecule model. Both the real and imaginary parts of dielectric permittivity are substantially increased at frequencies corresponding to intramolecular vibrations of atoms when each cluster of aqueous system adsorbs one argon atom. This effect disappears for the real part and becomes weak for the imaginary part of dielectric permittivity when there are two argon atoms added per cluster. In the region of intramolecular frequencies, the absorption coefficient of aqueous disperse systems containing argon increases as well. The reflection coefficient of the systems of water clusters that absorbed argon decreases in the frequency region of vibrations of molecules and increases in a frequency range corresponding to intramolecular vibrations. The power of radiation generated by cluster systems at the expense of thermal energy increases considerably when there is one adsorbed argon atom per cluster and decreases with a twofold increase in the number of argon atoms in clusters.     

IR spectra of aqueous disperse systems adsorbed atmospheric gases: 1. Nitrogen

Spectral characteristics of (H₂O) _i , N₂(H₂O) _i , and (N₂)₂(H₂O) _i cluster systems, where 10≤i≤50, are studied in the 0 ≤ ε ≤ 3500 cm^?1 frequency range with the molecular dynamics method on the basis of a flexible molecule model. After nitrogen is captured by an aqueous disperse system, the absorption of the IR radiation by this system increases owing to the enhancement of intramolecular vibrations. In general, the reflection of the outer IR radiation by nitrated aqueous disperse systems is attenuated; however, when the nitrogen concentration increases twofold, there is a tendency toward an increase in the fraction of reflected radiation. As the nitrogen concentration in a system of water clusters rises, the power of radiation emitted by the system increases significantly and the number of electrons interacting with the outer IR radiation decreases.     

Theoretical study of IR spectra of paraphenylenediamine

Normal coordinate analysis of the paraphenylenediamine (1,4-diaminobenzene, PPD) molecule has been carried out and complete interpretation of the vibrational spectrum is given for both trans and cis isomers. The reliable force field and electro-optical parameters of PPD have been determined by refinement in order to fit the experimental wavenumbers and intensities of PPD molecule. The initial force field parameters of PPD were refined from the corresponding parameters of aniline molecule. The initial values of bond dipole moments of the molecule were calculated by MINDO/3 method. The combination of the calculated IR spectra of trans and cis isomers of PPD is found to reproduce the experimental IR spectrum of solid PPD, satisfactorily, indicating that PPD exists as a mixture of both conformations.     

IR study of aqueous metal perchlorate solutions

Aqueous solutions of Mn(II), Co(II), Ni(II), and Zn(II) perchlorates, and for comparison, Mg(II) and Ca(II) perchlorates, have been studied by IR spectroscopy using HDO as an indicator. The investigations were carried out over the entire available concentration range of these salts. Computer deconvolution of the measured spectra demonstrates the effect of metal cations on the HDO molecules.