Search results for "Triatomic molecule"
showing 10 items of 16 documents
Extension of Walsh's rules to more general systems
1972
It is demonstrated that location of hydrogen atoms within bonding distance of a simple triatomic molecule can alter the order of energy levels relative to that of the parent system without significantly changing the behavior of the orbital energies under geometrical variation. As a result the ground state electronic configurations of H n AB2 systems often differ from those of triatomics with the same number of electrons and this fact is shown to be directly responsible for the existence of such distinctive geometrical structures as those possessed by cyclopropane, cyclopropyl and allyl cations and cyclopropene. Thus the familiar prescription of Walsh's rules which states that isoelectronic …
Application of time-resolved spectroscopy to concentration measurements in gas mixtures
2001
1296-2147; Concentration measurements using femtosecond Raman Induced Polarization Spectroscopy (RIPS) are performed in binary gas mixtures CO2-N2 and CO2-N2O at room temperature. The principle of these measurements is based on the nonlinear rotational time response of each molecular component of the mixture, The general form of this molecular response is a series of periodic transients with a period related to the rotational constant Be The relative strength of the individual responses allows an accurate determination of the concentration. Two techniques are presented using either two pulses (one pump and one probe) or three pulses (two pumps and one probe). (C) 2001 Academie des sciences/…
Analytic first and second derivatives for the CCSDT-n (n = 1–3) models: a first step towards the efficient calculation of CCSDT properties
2000
Analytic first and second derivatives of the energy are implemented for closed-shell systems described by the CCSDT-n (n=1, 1b, 2 and 3) and CC3 electron correlation models. A detailed discussion of the computational requirements of these calculations is given, along with diagrammatic formulas for all relevant quantities. The method is applied to calculate the nuclear magnetic shielding of H2O, CO and N2O and the structure and properties of propadienylidene.
Exchange interactions through hydrogen-bond bridges. Crystal structure, spectroscopic characterisation and magnetic properties of the complex [{Cu(en…
1998
Abstract The structure and spectroscopic and magnetic properties of [{Cu(en)}2(μ-egta)]·4H2O (H4egta = 3,12-bis(carboxymethyl)-6–9-dio 3,12-diazatetradecanedioic acid) are described. The compound is built of centrosymmetric neutral dimeric {[Cu(en)}2(μ-egta)] entities linked through hydrogen bonds involving water molecules. -NH2 groups and -CO2 groups, affording a three-dimensional framework. The egta anion displays an opened-up structure acting as a bridging ligand between two copper atoms. The coordination geometry about the metal atoms can be viewed as 4 + 1 + 1 (CuN3OO′O″ chromophores). The EPR spectra are indicative of an essentially dv−v ground state for the copper(II) ions. Magnetic …
Spectroscopic, magnetic, and electrochemical studies of a dimeric N-substituted-sulfanilamide copper(II) complex. X-ray and molecular structure of th…
2010
Abstract A dinuclear copper(II) complex with a N-substituted sulfonamide as ligand has been investigated. The new N-(pyridin-2-yl)biphenyl-4-sulfonamide ligand has been prepared and structurally characterized. The copper(II) complex has been synthesized and its crystal structure, magnetic properties and EPR spectra were studied in detail. The metal centers are bridged by four nonlinear triatomic NCN groups. The coordination geometry of the copper(II) ions in the dinuclear entity is distorted square planar with two N-pyridyl and two N-sulfonamido atoms. Magnetic susceptibility data show a moderate antiferromagnetic coupling, with −2 J = 284 cm−1. The EPR spectrum of the polycrystalline sampl…
Molecular electric quadrupole moments calculated with matrix dressed SDCI
2002
Abstract We have calculated the molecular electric quadrupole moment (MEQM) for the set of molecules N 2 , C 2 H 2 , CO, CO 2 , CS 2 , HF, and BH. We have used SR-SDCI and (SC) 2 -SR-SDCI methods and we have compared our results with high-level theoretical ones, including FCI values for HF and BH, and with experimental values. The calculated MEQM provides a test of the effect that the energy converged (SC) 2 dressing method brings to the SDCI wavefunctions. The results suggest that the (SC) 2 -SR-SDCI method can be a cost-effective and quite accurate method for the calculation of post-SCF effects on electric quadrupole moments.
On the theoretical determination of the electron affinity of ozone
1993
Multiconfigurational electron correlation methods have been analyzed in order to theoretically compute the electron affinity (EA) of ozone. The near-degeneracy correlation effects, which are so important in O3 and O 3 − , have been described using complete active space (CAS) SCF wave functions. Remaining dynamic correlation effects are computed using second-order perturbation theory (the CASPT2 method). The best calculated adiabatic value (including zero-point energy corrections), 2.19 eV, is about 0.09 eV larger than the experimental value. Comparative studies using size-consistent coupled pair functional approaches (CPF and ACPF) have also been performed. The harmonic frequencies in O 3 −…
Laser spatial profile effects in measurements of impulsive molecular alignment
2005
0953-4075; We use a non-intrusive technique based on a polarization scheme to probe the periodic alignment of the CO2 and N2 molecules induced by a strong laser pulse linearly polarized. A weak probe field experiences the birefringence resulting from the alignment of the molecules. By comparing the probe depolarization signal with the numerical simulation of the time-dependent Schrödinger equation, it is possible to quantify the alignment of the molecular sample. The modelling takes into account the spatial profile of the pump intensity. It allows from the alignment signal to determine the onset of saturation due to ionization, despite the intrinsic saturation of the alignment arising for a…
Laser-induced field-free alignment of the OCS molecule
2007
We investigate the dynamical alignment of jet-cooled OCS molecules induced by a short laser pulse. The alignment is measured through the orientational contribution of the optical Kerr effect using a second weak laser pulse as a probe. Maximum alignment is observed at conditions close to saturation of ionization. The results are analysed with a quantum mechanical model solving for the rotational dynamics.
Silicon Oxysulfide, OSiS: Rotational Spectrum, Quantum-Chemical Calculations, and Equilibrium Structure.
2011
Silicon oxysulfide, OSiS, and seven of its minor isotopic species have been characterized for the first time in the gas phase at high spectral resolution by means of Fourier transform microwave spectroscopy. The equilibrium structure of OSiS has been determined from the experimental data using calculated vibration-rotation interaction constants. The structural parameters (rO-Si = 1.5064 A and rSi-S = 1.9133 A) are in very good agreement with values from high-level quantum chemical calculations using coupled-cluster techniques together with sophisticated additivity and extrapolation schemes. The bond distances in OSiS are very short in comparison with those in SiO and SiS. This unexpected fi…