Vibrational Frequencies Of Ground Research Articles

Quantum chemical calculations and spectroscopic measurements of spectroscopic and thermodynamic properties of given uranyl complexes in aqueous solutions with possible environmental and industrial applications

A brief introduction into computational methodology and preliminary results for spectroscopic (excitation energies, vibrational frequencies in ground and excited electronic states) and thermodynamic (stability constants, standard enthalpies and entropies of complexation reactions) properties of some 1:1, 1:2 and 1:3 uranyl sulphato- and selenato- complexes in aqueos solutions will be given. The relativistic effects are included via Effective Core Potential (ECP), electron correlation via (TD)DFT/B3LYP (dispersion interaction corrected) and solvation is described via explicit inclusion of one hydration sphere beyond the coordinated water molecules. We acknowledge limits of this approximate description – more accurate calculations (ranging from semi-phenomenological two-component spin-orbit coupling up to four-component Dirac-Coulomb-Breit hamiltonian) and Molecular Dynamics simulations are in preparation. The computational results are compared with the experimental results from Time-resolved Laser-induced Fluorescence Spectroscopy (TRLFS) and UV-VIS spectroscopic studies (including our original experimental research on this topic). In case of the TRLFS and UV-VIS speciation studies, the problem of complex solution spectra decomposition into individual components is ill-conditioned and hints from theoretical chemistry could be very important. Qualitative agreement between our quantum chemical calculations of the spectroscopic properties and experimental data was achieved. Possible applications for geochemical modelling (e.g. safety studies of nuclear waste repositories, modelling of a future mining site) and analytical chemical studies (including natural samples) are discussed.

A unitary group based open-shell coupled cluster study of vibrational frequencies in ground and excited states of first row diatomics

The performance of recently introduced coupled cluster (CC) method exploiting the unitary group approach (UGA) to many-electron systems, truncated at the first order interacting space level [UGA-CCSD(is)] and using the 6-31G* basis set, in computations of equilibrium bond lengths and harmonic vibrational frequencies, is examined for a series of open-shell (OS) states of the first row diatomics and hydrides. Altogether, 48 distinct electronic states are considered for 9 diatomic hydrides (BeH, BH, CH, CH+, NH, NH+, OH, OH+ and FH) and 18 diatomics (BeF, BN, BO, C2, C2+, C2−, CN, CO, CO+, CF, N2+, NO, NO−, NF, O2, O2+, OF and F2+), involving both high and low spin cases. Very good agreement with the available experimental data is found in all cases, except when the experimental values are marked as ‘‘uncertain’’ or where only the ΔG(1/2) values of harmonic frequencies are available. For the so-called ‘‘difficult’’ systems, namely NO(X 2Π), O2(X 3Σg−), O2+(X 2Πg), OF (X 2Π) and F2+ (X 2Πg), the geometries and vibrational frequencies are also calculated using the TZ2P [5s4p2d] basis sets, and the results are compared with both the experiment and existing perturbation theory and CC results. All results indicate that UGA CCSD(is) represents a versatile, reliable and computationally affordable method that can handle a great variety of OS states, including OS singlets.

Site-selection spectroscopy and hole-burning of ionic dyes in amorphous hosts at low temperature

The hole-burning (HB) mechanism of the ionic dyes resorufin and cresyl violet was investigated in various glasses and polymers at liquid helium temperature. By means of hole-filling experiments the spectral distance of the photoproduct absorption maximum to that of the original molecule δ max was determined. It was observed that δ max and the electron-phonon coupling strength, S, increase with host polarity, Z, in the ionic dyes studied, whereas δ max and S are both independent of Z in the neutral free-base porphin molecule. A linear relation between δ max and S was found for all cases. The results suggest that these ionic dye systems undergo intermolecular photochemical hole-burning with high HB efficiency. Furthermore, two differently solvated species of resorufin in alcoholic glasses (ethanol and glycerol) were identified, and the vibrational frequencies of ground and first excited singlet states were obtained for both species. It is inferred that one of the species is hydrogen bonded to the host, whereas the other is a “free” resorufin molecule. Although hydrogen-bonding solvents enhance the HB efficiency, they are not necessary for the hole-burning process to occur.

Quantum Mechanical Consistent Force Field (QCFF/PI) Method: Calculations of Energies, Conformations and Vibronic Interactions of Ground and Excited States of Conjugated Molecules

AbstractThe extension of the Consistent Force Field approach to π electron systems is outlined. The quantum mechanical energy of π electrons is given as an analytical function of the molecular coordinates. It is shown that with this analytical description one can calculate efficiently equilibrium geometries and vibrational frequencies of ground and excited states of conjugated molecules. Application of the calculated geometry and vibrations to the analysis of vibronic structure is described. A preliminary account of the use of observed vibronic structure for determination of the geometry of excited electronic states is given.

Near-Ultraviolet Absorption Spectrum of m-Chlorobenzonitrile in Vapor Phase

The absorption spectrum of a molecule appears due to the transition between various vibrational levels of ground state to the different levels of the excited electronic states, and thus, is capable of giving detailed information regarding the vibrational frequencies of the upper electronic state and a few of the ground state. This short report presents the information about the 0,0 band and the vibrational frequencies of ground and excited electronic states of m-chlorobenzonitrile in vapor phase.