A NEW APPROACH TO THE DETECTION AND DETERMINATION OF o-CHLOROBENZYLIDENE-MALONONITRILE (CS) AND ITS CHEMICAL RELATIVES

ABSTRACT

o-Chlorobenzylidenemalononitrile (CS-gaz) has been found to react with KCN in DMSO and to form practically quantitatively a stable 1:1 adduct of carbanionic structure. The conversion results in the appearance of two very strong ν ^s _C≡N and ν ^as _C≡N IR bands of the dicyanomethide fragment of the adduct at 2161 cm^?1 and 2106 cm^?1, respectively. These bands can be used to detect selectively and to determine quantitatively CS and its chemical relatives, including in the presence of large quantities of other substances.     

High-resolution rovibrational analysis of vibrational states of A2 symmetry of the dideuterated methane CH2D2: the levels ν 5 and ν 7 + ν 9

The infrared spectrum of the CH₂D₂ molecule has been measured in the region 900–1500?cm^?1 on a Bomem DA002 Fourier transform spectrometer with a resolution of 0.0024?cm^?1 (FWHM, unapodized). Transitions belonging to the hot bands ν ₇?+?ν₉?ν ₇, ν₇?+?ν₉? ν ₉, ν₅?+?ν₇?ν₅, and ν₅?+?ν₉?ν₅ were extracted from the recorded spectra to determine the rovibrational energies of the A₂ symmetry vibrational states (v ₇?=?v ₉?=?1) at 2329.698?cm^?1 and (v ₅ ?=?1) at 1331.409?cm^?1. Vibrational energies as well as rotational and centrifugal distortion parameters of the (v ₇?=?v ₉=1) and (v ₅?=?1) states were determined that reproduce the experimental rovibrational energy levels of the (v ₇?=?v ₉?=?1) and (v ₅?=?1) vibrational states with a d _rms deviation of 0.0017 and 0.0006?cm^?1, respectively. The results are discussed in relation to the equilibrium structure of methane, which is redetermined here from the experimental data, and in relation to its potential hypersurface and anharmonic vibrational dynamics.     

Assignment of a perturbation in the FT-ICLAS spectrum of 12C2H2 around 12 709.5 cm−1

The vibrational state perturbing the J = 17 and 18 rotational states of the zero-order v ₁ + 3v ₃ state of ¹²C₂H₂ is assigned to the state with vibrational energy predicted at G _ν = 12 685.1 cm^?1 using the cluster model (El Idrissi, M. I., Liévin, J., Campargue, A. and Herman, M., 1999, J. chem. Phys., 110, 2074). The assignment is discussed also in terms of the very special pressure shift behaviour demonstrated previously for absorption lines reaching these levels (Herregodts, F., Hepp, M., Hurtmans, D., Vander Auwera, J. and Herman, M., 1999, J. chem. Phys., 111, 7961). The experimental information arising from a set-up newly running at ULB, called FT-ICLAS brings decisive information in the assignment process. This set-up is described briefly.     

Study of the lowest electronic states of Xe2, XeKr, and XeAr molecules by the method of multiphoton resonance ionization

The spectra of Xe₂, XeKr, and XeAr molecules in the range 66 500–68 800 cm^?1 are obtained by the methods of (2 + n) and (3 + n) (n = 1, 2, 3) resonance multiphoton ionization during the registration of molecular and atomic ions. The combining of two-and three-photon resonance excitations of Xe₂ molecules makes it possible to obtain the spectra caused by transitions from the ground state X0 _g ⁺ to the excited states of Xe*6s[3/2] _1,2 ^o Xe¹ S ₀ molecules both of the even (0 _g ⁺ , 1 _g ) and of the odd (B0 _u ⁺ , B′1 _u , 2 _u ) symmetries. The data on the Ω = 2 _u state of the Xe₂ molecule with the dissociation limit Xe*6s[3/2] ₂ ^o + Xe¹ S ₀ and on the Ω = 1 state of the XeAr molecule with the dissociation limit Xe*6s[3/2] ₁ ^o + Ar¹ S ₀ are obtained for the first time. The potential curve of the excited 2 _u state of the Xe*6s[3/2] ₂ ^o Xe¹ S ₀ molecule is repulsive and intersects the potential curve of the B0 _u ⁺ state of the Xe*6s[3/2] ₁ ^o Xe¹ S ₀ molecule. In the case of the three-photon excitation, it is observed that all the bands in the spectra of XeKr and XeAr molecules are broadened and are shifted, which indicates that, in an intense light field, the influence of the dynamic Stark effect is significant.     

The equilibrium geometry of the SC3H radical: an ab initio study

The SC₃H radical is known by experiment to have a linear equilibrium structure, but even rather high-level ab initio computations give a bent equilibrium geometry. A theoretical study of the SCCCH radical has been carried out in order to analyse the influence of several factors in the computed equilibrium structure. Quadratic configuration interaction QCISD(T) and restricted coupled cluster RCCSD(T) computations have been performed in combination with large basis sets. Spin-orbit effects have been taken into account through the Breit-Pauli Hamiltonian using multi-configuration SCF and configuration interaction wavefunctions. Our final results indicate that the equilibrium structure must be linear, in agreement with the experimental studies [McCarthy, M. C., Vrtilek, J. M., Gottlieb, C. A., Wang, W., and Thaddeus, P., 1994, Astrophys. J., 431, L127; Hirahara, Y., Ohshima, Y, and Endo, Y, 1994, J. chem. Phys., 101, 7342]. Both spin-orbit and electron correlation effects appear to be of comparable importance, but an adequate computation of the correlation energy has been much more difficult and has ultimately required basis set extrapolations.     

Real figure of two-dimensional spin-echo NMR spectra for a homonuclear two-spin system in rotating solids

Two-dimensional (2D) spin-echo NMR experiments have been carried out on polycrystalline [2,3-¹³C₂]-alanine under magic-angle sample spinning (MAS) conditions, so that two unusual resonance lines emerged along the F₁ axis (Kuwahara, D., Nakai, T., Ashida, J., and Miyajima, S., 1999, Chem. Phys. Lett., 305, 35). To examine the spectral structure observed in the F₁ direction more closely the 2D NMR experiment was undertaken using a sufficiently small t_l increment, yielding many more resonance lines on a spectrum sliced along the F₁ axis. The line distribution had a very unique and interesting structure. To elucidate the line positions theoretically, the signal for the 2D spin-echo experiment performed with any t₁ increment was calculated analytically for a homonuclear two-spin-1/2 system undergoing MAS. Virtually six resonance lines (exactly 12 resonance lines) occurred on a spectrum sliced along the F₁ axis. In addition, it was demonstrated that the intensities of some resonance lines were largely dependent on the dipolar interaction.     

Theoretical reason for the lack of influence of 1H–14N cross-relaxation on the water proton T 1 NMRD profile in slow tumbling proteins

For immobilized protein the water proton T ₁-NMRD profile displays three enhanced relaxation peaks (QP). For slow tumbling proteins these relaxation peaks are not experimentally observed. However, the theoretically determined QP effect on the amide proton T ₁-NMRD profile displays a distorted Lorentzian dispersion profile. The question arises as to whether there is also a distortion of the water-proton T ₁-NMRD profile due to QP. The model of Sunde and Halle [J. Magn. Reson. 203, 257 (2010)] predicts a decreasing QP relaxation contribution and, with the aid of a model for tumbling proteins [P.-O. Westlund, Phys. Chem. Chem. Phys, 12, 3136 (2010)], it is shown that the QP effect is absent in water-proton T ₁-NMRD profiles for slow tumbling proteins with τ_R?I.     

Singlet–triplet transitions in three-atomic molecules studied by time-dependent MCSCF and density functional theory

Singlet–triplet transition moments and phosphorescence lifetimes have been calculated for the three-atomic molecules HCN, O₃, H₂O, H₂S, GeF₂, GeCl₂ and GeBr₂ by time-dependent density functional theory (DFT) utilizing quadratic response functions in order to qualify DFT which recently has become available for studies of this kind [TUNELL, I., Rinkevivius, Z., VAHTRAS, O., SALEK, P., HELGAKER, T., and ÅGREN, H., 2003, J. chem. phys., 119, 11024]. Comparison with ab initio and experimental data indicates that DFT exhibit results of similar quality as explicitly correlated methods which indicates that it indeed is a viable approach for singlet–triplet transitions. O₃ provides an intriguing example in that a systematic investigation of the singlet–triplet transition moment of its Wulf band indicates a clear advantage of the DFT technique despite the multiconfigurational character of the electronic structure of this molecule. The electronic spin–spin coupling and the hyperfine nuclear coupling constants have also been calculated in order to further characterize the triplet state in the spectra of the investigated systems.     

Conformational analysis of <Emphasis Type="Italic">o</Emphasis>-allylphenol by density functional and IR spectroscopy methods

The two-dimensional cyclic potential energy surfaces for internal rotation of the allyl substituent and its vinyl fragment in o-allylphenol (o-APh) depending on the OH group orientation relative to the allyl substituent were constructed by a B3LYP/6-31G method. It is shown that o-APh exists in the gas phase as a mixture of eight non-planar rotamers (A, B, C, D, E, F, G, and H) and their eight optical isomers (A ₁, B ₁, C ₁, D ₁, E ₁, F ₁, G ₁, and H ₁). An intramolecular H-bond (IHB) O–H...π occurs only in four rotamers (A, B, A ₁, and B ₁). The content of such rotamers in the gas phase is 47.2% (as calculated by the B3LYP/cc-pVTZ method). Taking into account the solvation effect in the polarizable continuum model (PCM) for a solution of o-APh in cyclohexane decreases the total content of rotamers with an IHB (A and B) to 37.7%. The ratio of rotamers with OH groups bonded by an IHB and with free OH groups that is predicted theoretically agrees with the value measured experimentally from IR spectra of o-APH in CCl₄ solution.     

An efficient basis set representation for calculating electrons in molecules

ABSTRACT

The method of McCurdy, Baertschy, and Rescigno, J. Phys. B, 37, R137 (2004) [1 C.W. McCurdy, M. Baertschy, and T.N. Rescigno, J. Phys. B 37, R137 (2004).[Crossref], [Web of Science ®] , [Google Scholar]] is generalised to obtain a straightforward, surprisingly accurate, and scalable numerical representation for calculating the electronic wave functions of molecules. It uses a basis set of product sinc functions arrayed on a Cartesian grid, and yields 1 kcal/mol precision for valence transition energies with a grid resolution of approximately 0.1 bohr. The Coulomb matrix elements are replaced with matrix elements obtained from the kinetic energy operator. A resolution-of-the-identity approximation renders the primitive one- and two-electron matrix elements diagonal; in other words, the Coulomb operator is local with respect to the grid indices. The calculation of contracted two-electron matrix elements among orbitals requires only O(Nlog?(N)) multiplication operations, not O(N⁴), where N is the number of basis functions; N = n³ on cubic grids. The representation not only is numerically expedient, but also produces energies and properties superior to those calculated variationally. Absolute energies, absorption cross sections, transition energies, and ionisation potentials are reported for 1- (He⁺, H⁺₂), 2- (H₂, He), 10- (CH₄), and 56-electron (C₈H₈) systems.     

Crystal Structures of Tetrakis‐(4‐chlorophenylthio)‐butatriene and Tetrakis‐(tert‐butylthio)‐butatriene

Tetrakis‐(4‐chlorophenylthio)‐butatriene (3a) and tetrakis‐(tert‐butylthio)‐butatriene (3b) were synthesized, and their crystal structures were determined. The compound 3a is monoclinic, space group P2₁/c, a=6.9785(8), b=8.6803(9), c=22.884(2) Å, β=93.887(6)^o, V=1383.0(3) ų, Z=2. The compound 3b is monoclinic, space group P2₁/n, a=11.0615(6), b=10.8507(4), c=11.2717(6) Å, β =116.427(2)^o, V=1211.5(1) ų, Z=4. The title compounds 3a and 3b reside on an inversion center so that only half of the molecule is crystallographically unique. Both compounds are not planar. The crystal structures of 3a and 3b have cumulated double bonds. The C7–C8–C8ⁱ and C5–C6–C6ⁱ angles that show the linearity in both structures, respectively, are 176.4(3)° in 3a and 175.6(2)° in 3b.     

Proton spin-lattice relaxation in aqueous ionic solutions

The proton spin-lattice relaxation time, T ₁, has been measured for aqueous solutions of sodium, potassium, rubidium and magnesium chlorides up to a concentration of about 4N at 25°c. The sodium and the magnesium chloride solutions were also measured at 60°c and 100°c. The variation of 1/T ₁ is not linear with concentration, at least above about ¼N, in contrast with previous reports [1, 2]. The behaviour depends markedly on the nature of the salt and on the temperature. It is shown that almost the whole of the variation of T ₁ as compared with that of water can be directly and simply related to the corresponding changes in the shear viscosity of the solutions. It is noted that the viscosity correction is better the higher the temperature of the solution.     

Magnetic field dependence of Sommerfeld coefficient and penetration depth in NdFeAsO1−XFX single crystal

Anisotropic properties of Sommerfeld coefficient and penetration depth for single crystal NdFeAsO_1?xF_x has been studied by using modified phenomenological Ginzburg–Landau (GL) theory. In the above two-band superconducting system, the calculated value of Sommerfeld coefficient shows very close proximity with the experimental result as reported by Welp. Further, anisotropic ratio of penetration depth also calculated and reported for this system. The results of anisotropic properties of the above superconducting system implied that modified GL-theory in the form presented here can be applicable to the above superconducting system.     

On the trace and the relativistic scalar products involving Dirac matricesγ i and the 4 × 4 unit matrix

In this paper we have dealt with the relativistic scalar products likeγ _i uγ _i,Tr(γ _i u) Tr(γ _i v) and Tr(γ _i γ _j v). Here any string likeu andv involve Dirac matrices in the manneru=Π _n ^r=1 a _r where the element \(a_r = a_{r_i } \gamma _i + ia_{r_5 }\) i.e.,a _r in general involves a term \(ia_{r_5 }\) which is multiplied by a 4 × 4 unit matrix. We have further evaluated Tr (γ _b u) Tr (γ _b v) where the suffix ‘b’, unlike the dummy suffixesi andj, does not imply any summation and can assume any specific value from 1 to 5. Some reduction formulae for the evaluation of Tr (γ₅ u) and Tr(u) have been obtained in this paper.     

The absorption spectrum of 12C2D2 in the 10000–12500 cm−1 spectral region

The absorption spectrum of dideuteroacetylene has been recorded by intracavity laser absorption spectroscopy (ICLAS) in the 10 200–12 500cm^?1 spectral region. Among 25 absorption bands of ¹²C₂D₂ rotationally analysed in this spectral region, 17 are newly observed. They include one II_u-Σ⁺ _g and thirteen Σ⁺ _u-Σ⁺ _g bands starting from the vibrational ground state and eleven hot bands from the V ₄ = 1 and V ₅ = 1 lower states. The rotational structure of two excited levels is affected by a strongly J-dependent interaction with a perturber which induces intensity transfer to extra lines. The coupling is identified as a I-resonance interaction with δ_u dark states and the vibrational assignment of the perturbers is discussed. Two Σ-Σ bands of the ¹²C¹³ CD₂ species, present in natural abundance in the sample, could also be identified and rotationally analysed. Most of the corresponding excited vibrational levels of ¹²C₂D₂ were unambiguously assigned using the polyad model [Herman, M., el idrissi, M. I., Pisarchik, A., Campargue, A., Gaillot, A.-C., Biennier, L., di lonardo, G. and Fusina, L., 1998, J. chem. Phys., 108, 1377] which allows vibrational energies and B _V rotational constants to be predicted. In particular the previously highlighted 1/244 anharmonic resonance is confirmed by energy and intensity features in several {(V ₁, V ₂, V ₃, V ₄ = 0, V ₅ = 0),(V ₁ ?1, V ₂ + 1, V ₃ V ₄ = 2, V ₅ = 0)} dyads. Significant deviations between predicted and experimental energy levels are observed for a few levels and discussed.