Band Contours Research Articles

Theoretical prediction of the electronic structure, bonding behavior and elastic moduli of scandium intermetallics

We report the structural, electronic, bonding, elastic and mechanical properties of nine scandium intermetallic compounds, ScTM (TM = Co, Rh, Ir, Ni, Pd, Pt, Zn, Cd and Hg), using ab initio density functional theory with the generalized gradient approximation for exchange and correlation potentials. The calculated structural parameters, such as the lattice constant (a0), bulk modulus (B) and its pressure derivative (B0) and elastic constants, are calculated using the CsCl-(B2 phase) structure. The electronic and bonding properties of the ScX compounds are quantitatively analyzed using band structures, DOS, Fermi surfaces and contour plots. The mechanical properties and ductile behaviors of these compounds are also predicted based on the calculated elastic constants.

Correlation Between Hydroxide ion Dynamics and Transport Properties of Hydroxide/Chloride Melts According to Raman Spectroscopy Data

UDC 541.454;543.42;535.375.5 Using data obtained in analysis of the band contour for the totally symmetric stretching vibration of the OH - anion in Raman spectra of hydroxide/chloride ionic melts, a correlation has been established between the orientational relaxation time and effective moment of inertia of the hydroxide ion and the transport properties of the electrolyte. Study of the structure of ionic compounds and its controlling infl uence on physical and chemical properties is one of the fundamental scientifi c problems in physical chemistry. Today the appearance of new and improvement of conventional experimental methods for studying the structure of matter and also creation of high-tech device components has permitted considerable expansion of the range of systems that can be studied, including high-temperature ionic melts. Development of methodological approaches has led to a signifi cant increase in the amount of information that can be extracted and an increase in the reliability of this information. Raman spectroscopy is a physical method for investigation of matter which, based on recorded vibrational spectra of the analyte system, allows us to carry out structural analysis, to determine the vibrational frequencies, and to calculate force constants and the moment of inertia of a molecule and the rates of relaxation processes. In contrast to x-ray diffraction and neutron diffraction methods, determining the structure of materials (the symmetry type, the interatomic distances, the coordination numbers), the Raman spectroscopy method allows us to obtain a much greater amount of information: the recorded vibrational frequencies correspond to the position of the vibrational levels in the molecule, the width of the vibrational bands contain information about its rotational motion, and the intensity of the Raman spectra directly determines the bond ionicity or covalency (1, 2). Today a methodological approach has been developed that allows us, from analysis of the contour of the vibrational bands and the width of their isotropic and anisotropic components, to obtain important information about the dynamics of the particles in the picosecond time range (1-4). It has been shown (4) that information about relaxation processes can be obtained by calculating the temporal correlation functions, the vibrational and orientational relaxation times for the structural units. Unique information on estimation of the moments of inertia of particles, which is practically inaccessible by other methods for studying the condensed state of matter and which can be obtained only using high-resolution rotational spectra of gas molecules, can be extracted by analyzing the shape of the contour of vibrational bands using the spectral moments method (4). According to this method, the moment of inertia can be calculated from the equation (3): I = 6kT/4π 2 c 2 Mor(2),

Density functional study of XRh (X = Sc, Y, Ti and Zr) intermetallic compounds

Systematic first principle calculations have been performed to study the structural, electronic, elastic, bonding and mechanical properties of ScRh, YRh (group III), TiRh and ZrRh (group IV) with the generalized gradient approximation for exchange and correlation. Ground state properties such as lattice constant (a0), bulk modulus (B), its pressure derivative (B0) and elastic constants are calculated. The calculated values of lattice constant are in good agreement with the experimental and theoretical results. The electronic and bonding patterns of the two groups of compounds have been analysed quantitatively from band structure, Fermi surfaces and contour plots. The ‘d’ states of X (X=Sc, Y, Ti and Zr) atoms play an essential role in differentiating the bonding behaviour of these two groups of compounds. The study of charge density plots reveals that group IV intermetallics are more ionic than group III intermetallics. Poisson’s ratio (σ), Young’s moduli (E), shear moduli (GH) and the ratio of elastic anisotropy factor (A) are also estimated. Ductility for these compounds is further analysed by using Pugh’s criteria, Cauchy pressure (C12–C44) and Frantsevich rule. Amongst all these intermetallics, ZrRh is found to be most ductile due to the presence of strong metallic bonding.

Infrared and Raman spectra, adjusted r0 structural parameters, and vibrational assignment of isopropyl isocyanide

Infrared spectra (3200–220cm−1) of gaseous and Raman spectra (3200–40cm−1) of liquid isopropyl isocyanide ((CH3)2CHNC) have been recorded. By utilizing the microwave rotational constants combined with the structural parameters predicted from MP2(full)/6-311+G(d,p) calculations, adjusted r0 parameters have been obtained for isopropyl isocyanide. The heavy atom distances in Å are: r (C1N2)=1.176(3), r (N2C3)=1.437(3), r (C3C4,5)=1.525(5) and the angles in (°) are ∠C1N2C3=178.6(5); ∠N2C3C4,5=109.4(5); ∠C4C3C5=113.0(5). A complete vibrational assignment is proposed for isopropyl isocyanide based on infrared band contours, relative intensities, depolarization values, and group frequencies. The vibrational assignments were supported by normal coordinate calculation utilizing the force constants from ab inito MP2(full)/6-31G(d). The results are discussed and compared to those obtained for some similar molecules.

Excited-State Structure, Vibrations, and Nonradiative Relaxation of Jet-Cooled 5-Fluorocytosine

The S0 → S1 vibronic spectrum and S1 state nonradiative relaxation of jet-cooled keto-amino 5-fluorocytosine (5FCyt) are investigated by two-color resonant two-photon ionization spectroscopy at 0.3 and 0.05 cm(–1) resolution. The 0(0)(0) rotational band contour is polarized in-plane, implying that the electronic transition is (1)ππ*. The electronic transition dipole moment orientation and the changes of rotational constants agree closely with the SCS-CC2 calculated values for the (1)ππ* (S1) transition of 5FCyt. The spectral region from 0 to 300 cm(–1) is dominated by overtone and combination bands of the out-of-plane ν1′ (boat), ν2′ (butterfly), and ν3′ (HN–C6H twist) vibrations, implying that the pyrimidinone frame is distorted out-of-plane by the (1)ππ* excitation, in agreement with SCS-CC2 calculations. The number of vibronic bands rises strongly around +350 cm(–1); this is attributed to the (1)ππ* state barrier to planarity that corresponds to the central maximum of the double-minimum out-of-plane vibrational potentials along the ν1′, ν2′, and ν3′ coordinates, which gives rise to a high density of vibronic excitations. At +1200 cm(–1), rapid nonradiative relaxation (k(nr) ≥ 10(12) s(–1)) sets in, which we interpret as the height of the (1)ππ* state barrier in front of the lowest S1/S0 conical intersection. This barrier in 5FCyt is 3 times higher than that in cytosine. The lifetimes of the ν′ = 0, 2ν1′, 2ν2′, 2ν1′ + 2ν2′, 4ν2′, and 2ν1′ + 4ν2′ levels are determined from Lorentzian widths fitted to the rotational band contours and are τ ≥ 75 ps for ν′ = 0, decreasing to τ ≥ 55 ps at the 2ν1′ + 4ν2′ level at +234 cm(–1). These gas-phase lifetimes are twice those of S1 state cytosine and 10–100 times those of the other canonical nucleobases in the gas phase. On the other hand, the 5FCyt gas-phase lifetime is close to the 73 ps lifetime in room-temperature solvents. This lack of dependence on temperature and on the surrounding medium implies that the 5FCyt nonradiative relaxation from its S1 ((1)ππ*) state is essentially controlled by the same ~1200 cm(–1) barrier and conical intersection both in the gas phase and in solution.

Vibrational-Rotational Interaction in Molecules of the Spherical Top Type

We show that, in the Raman spectrum of very low-density gases, the Q branch of the nu1 band of methane and deuteromethane has asymmetric contour. With increase in the gas density, the band contour becomes more symmetric and broadens. The band shape is described by the Voigt curve. Possible mechanisms of the vibrational broadening of v1 – dephasing and intermode exchange of vibrational energy – are analyzed. Both mechanisms may be efficient in the band broadening.

Low-lying excited states and nonradiative processes of 9-methyl-2-aminopurine.

The UV spectrum of the adenine analogue 9-methyl-2-aminopurine (9M-2AP) is investigated with one- and two-color resonant two-photon ionization spectroscopy at 0.3 and 0.05 cm(-1) resolution in a supersonic jet. The electronic origin at 32,252 cm(-1) exhibits methyl torsional subbands that originate from the 0A1'' (l = 0) and 1E(″) (l = ±1) torsional levels. These and further torsional bands that appear up to 00 (0)+230 cm(-1) allow to fit the threefold (V3) barriers of the torsional potentials as |V3''|=50 cm(-1) in the S0 and |V3'|=126 cm(-1) in the S1 state. Using the B3LYP density functional and correlated approximate second-order coupled cluster CC2 methods, the methyl orientation is calculated to be symmetric relative to the 2AP plane in both states, with barriers of V3''=20 cm(-1) and V3'=115 cm(-1). The 00 (0) rotational band contour is 75% in-plane (a/b) polarized, characteristic for a dominantly long-axis (1)ππ(*) excitation. The residual 25% c-axis polarization may indicate coupling of the (1)ππ(*) to the close-lying (1)nπ(*) state, calculated at 4.00 and 4.01 eV with the CC2 method. However, the CC2 calculated (1)nπ oscillator strength is only 6% of that of the (1)ππ(*) transition. The (1)ππ(*) vibronic spectrum is very complex, showing about 40 bands within the lowest 500 cm(-1). The methyl torsion and the low-frequency out-of-plane ν1' and ν2' vibrations are strongly coupled in the (1)ππ(*) state. This gives rise to many torsion-vibration combination bands built on out-of-plane fundamentals, which are without precedence in the (1)ππ(*) spectrum of 9H-2-aminopurine [S. Lobsiger, R. K. Sinha, M. Trachsel, and S. Leutwyler, J. Chem. Phys. 134, 114307 (2011)]. From the Lorentzian broadening needed to fit the 00 (0) contour of 9M-2AP, the (1)ππ(*) lifetime is τ ⩾ 120 ps, reflecting a rapid nonradiative transition.

Using 2D correlation analysis to enhance spectral information available from highly spatially resolved AFM-IR spectra

The recent combination of atomic force microscopy and infrared spectroscopy (AFM-IR) has led to the ability to obtain IR spectra with nanoscale spatial resolution, nearly two orders-of-magnitude better than conventional Fourier transform infrared (FT-IR) microspectroscopy. This advanced methodology can lead to significantly sharper spectral features than are typically seen in conventional IR spectra of inhomogeneous materials, where a wider range of molecular environments are coaveraged by the larger sample cross section being probed. In this work, two-dimensional (2D) correlation analysis is used to examine position sensitive spectral variations in datasets of closely spaced AFM-IR spectra. This analysis can reveal new key insights, providing a better understanding of the new spectral information that was previously hidden under broader overlapped spectral features. Two examples of the utility of this new approach are presented. Two-dimensional correlation analysis of a set of AFM-IR spectra were collected at 200-nm increments along a line through a nucleation site generated by remelting a small spot on a thin film of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). There are two different crystalline carbonyl band components near 1720cm−1 that sequentially disappear before a band at 1740cm−1 due to more disordered material appears. In the second example, 2D correlation analysis of a series of AFM-IR spectra spaced every 1μm of a thin cross section of a bone sample measured outward from an osteon center of bone growth. There are many changes in the amide I and phosphate band contours, suggesting changes in the bone structure are occurring as the bone matures.

Cavity Ringdown Spectroscopy of the Hydroxy-Methyl-Peroxy Radical

We report vibrational and electronic spectra of the hydroxy-methyl-peroxy radical (HOCH2OO(•) or HMP), which was formed as the primary product of the reaction of the hydroperoxy radical, HO2(•), and formaldehyde, HCHO. The ν1 vibrational (OH stretch) spectrum and the à ← X̃ electronic spectrum of HMP were detected by infrared cavity ringdown spectroscopy (IR-CRDS), and assignments were verified with density functional calculations. The HMP radical was generated in reactions of HCHO with HO2(•). Free radical reactions were initiated by pulsed laser photolysis (PLP) of Cl2 in the presence of HCHO and O2 in a flow reactor at 300-330 Torr and 295 K. IR-CRDS spectra were measured in mid-IR and near-IR regions over the ranges 3525-3700 cm(-1) (ν1) and 7250-7800 cm(-1) (à ← X̃) respectively, at a delay time 100 μs after photolysis. The ν1 spectrum had an origin at 3622 cm(-1) and exhibited partially resolved P- and R-branch contours and a small Q-branch. At these short delay times, spectral interference from HOOH and HCOOH was minimal and could be subtracted. From B3LYP/6-31+G(d,p) calculations, we found that the anharmonic vibrational frequency and band contour predicted for the lowest energy conformer, HMP-A, were in good agreement with the observed spectrum. In the near-IR, we observed four well spaced vibronic bands, each with partially resolved rotational contours. We assigned the apparent origin of the à ← X̃ electronic spectrum of HMP at 7389 cm(-1) and two bands to the blue to a progression in ν15', the lowest torsional mode of the à state (ν15' = 171 cm(-1)). The band furthest to the red was assigned as a hot band in ν15″, leading to a ground state torsional frequency of (ν15″ = 122 cm(-1)). We simulated the spectrum using second order vibrational perturbation theory (VPT2) with B3LYP/6-31+G(d,p) calculations at the minimum energy geometries of the HMP-A conformer on the X̃ and à states. The predictions of the electronic origin frequency, torsional frequencies, anharmonicities, and rotational band contours matched the observed spectrum. We investigated the torsional modes more explicitly by computing potential energy surfaces of HMP as a function of the two dihedral angles τHOCO and τOOCO. Wave functions and energy levels were calculated on the basis of this potential surface; these results were used to calculate the Franck-Condon factors, which reproduced the vibronic band intensities in the observed electronic spectrum. The transitions that we observed all involved states with wave functions localized on the minimum energy conformer, HMP-A. Our calculations indicated that the observed near-IR spectrum was that of the lowest energy X̃ state conformer HMP-A, but that this conformer is not the lowest energy conformer in the à state, which remains unobserved. We estimated that the energy of this lowest conformer (HMP-B) of the à state is E0 (Ã, HMP-B) ≈ 7200 cm(-1), on the basis of the energy difference E0(HMP-B) - E0(HMP-A) on the à state computed at the B3LYP/6-31+G(d,p) level.

Manifestation of resonance dipole-dipole interaction in spectra of low-temperature molecular mixtures of C2F6 in CF4 and CF4 in C2F6

We have measured IR absorption spectra of solutions C2F6 in CF4 (T = 178 K) and CF4 in C2F6 (T = 173 K) in the overtone range of the spectrum. We have studied how the resonance dipole-dipole interaction affects the formation of contours of bands that correspond to transitions to states involving the vibrations ν10(C2F6) and ν3(CF4), which are strong in the dipole absorption. For the system C2F6 in liquid CF4, the state ν2 + ν10(C2F6) resonantly interacts with the state ν2(C2F6) + ν3(CF4), and, for the system CF4 in liquid C2F6, the state ν1 + ν3(CF4) resonantly interacts with the state ν1(CF4) + ν10(C2F6). The contours of the bands ν2 + ν10 (C2F6) in the spectrum of the mixture with CF4 and of the bands ν1 + ν3(CF4) in the spectrum of the mixture with C2F6 have been calculated.

IR spectroscopic analysis of the new organic silver complex C13H13N4OAg

IR analysis in the frequency range 400–4000cm−1 is used here to investigate the changes in different modes of thermally treated new metal complex (diphenyl carbazide silver complex DPCAg, C13H13N4OAg) during the glass transition at 91°C and the high temperature phase transition at 167°C. These two phase transitions in this new metal compound are studied here by detecting the changes in some IR spectroscopic parameters (e.g., mode shift, band contour, peak height and peak intensity) during the elevation of temperature. All of the vibrations of DPCAg were found to be due to ionic fundamentals 3311cm−1, 3097cm−1, 3052cm−1, 1677cm−1, 1602cm−1, 1492cm−1, 1306cm−1, 1252cm−1, 887cm−1 and 755cm−1. The results obtained can be considered as the first spectroscopic analysis of this new metal complex. These results strongly confirmed that the thermally treated DPCAg transverse a glass transition at 91°C and a high temperature phase transition at 167°C. Anomalous spectroscopic changes near the glass transition temperature Tg could be recorded. A temperature dependence of peak intensity of the two modes 810cm−1 and 3440cm−1 could be observed beyond Tg. Also, the high temperature phase modification at 167°C showed anomalous change in the spectroscopic parameters before and after the phase transition process. A proposed silver position in the new silver complex DPCAg has been presented.

Retro reflection of electrons at the interface of bilayer graphene and superconductor

Electron reflection at an interface is a fundamental quantum transport phenomenon. The most famous electron reflection is the electron→hole Andreev reflection (AR) at a metal/superconductor interface. While AR can be either specular or retro-type, electron→electron reflection is limited to only the specular type. Here we show that electrons can undergo retro-reflection in bilayer graphene (BLG). The underlying mechanism for this previously unknown process is the anisotropic constant energy band contour of BLG. The electron group velocity is fully reversed upon reflection, causing electrons to be retro-reflected. Utilizing a BLG/superconductor junction (BLG/S) as a model structure, we show that the unique low energy quasiparticle nature of BLG results in two striking features: (1) AR is completely absent, making BLG/S 100% electron reflective; (2) electrons are valley-selectively focused upon retro-reflection. Our results suggest that BLG/S is a valley-selective Veselago electron focusing mirror which can be useful in valleytronic applications.

Raman and infrared spectra, r0 structural parameters, and vibrational assignments of (CH3)2PX where X = H, CN, and Cl

The infrared (3500–80cm−1) and Raman spectra (3500–40cm−1) of gas/or liquid and solid (CH3)2PX with X=H (DMH), CN (DMCN) and Cl (DMCl) as well as (CD3)2PH have been recorded and complete vibrational assignments are given for all three molecules. To support the spectroscopic study, ab initio calculations by the Møller–Plesset perturbation method to second order MP2(full) and density functional theory calculations by the B3LYP method have been carried out. The infrared intensities, Raman activities, vibrational frequencies and band contours have been predicted from MP2(full)/6-31G(d) calculations and these theoretical quantities are compared to experimental ones when available. By utilizing the previously reported microwave rotational constants for DMH and DMCN along with the MP2(full)/6-311+G(d,p) predicted values, adjusted r0 structural parameters for DMH and DMCN have been determined. The heavy atom parameters for DMH are: r0(PC3,4)=1.8477(30)Å, ∠CPC=99.88(50)° and for DMCN: r0(NC)=1.159(3), r0(CP)=1.790(3), r0(PC4,5)=1.841(3)Å, ∠NCP=175.7(5), ∠CPC4,5=97.9(5) and ∠CPC=100.7(5)°. Barriers to internal rotation are reported. The experimental values are compared to the corresponding values of some similar molecules whenever possible.

Raman Scattering Study on Vibrational Modes and Structure of Lanthanum Tellurite Glasses

Raman spectra of xLa2O3-(1−x)TeO2 (x=0, 0.05, 0.10, 0.15, 0.20, and 0.25) lanthanum tellurite glasses were measured and analyzed over the entire glass-forming region in an effort to quantitatively follow the structural changes caused by lanthanum oxide variation. For the first time, systematic intensity measurements have been performed to elucidate the composition induced structural changes in the high-frequency stretching vibration region and a possible mechanism was proposed. The network structure of the glasses is formed by mixing TeO4 trigonal bipyramid and TeO3 trigonal pyramid units. The change of the lanthanum oxide content results in conversion of the TeO4 units to TeO3 units with a varying number of non-bridging oxygen atoms. Analysis of the Raman band contours in terms of vibrations due to different oxygen bridged trigonal bipyramid and trigonal pyramid tellurite structural units, allowed to calculate the relative amounts of the species involved in the structural changes with composition. The fraction of the terminal oxygen atoms has been estimated from the Raman intensities with the aid of a structural model concerning the structure of tellurite network systems. The simulation of the experimental density of lanthanum tellurite glasses with modifier content up to 25% revealed that the short range order building units assumed here are sufficient to account for the overall structure in these glasses.

Computer analysis of vibrational spectra of aqueous ethanol solutions

Results of decomposition of vibrational spectra for aqueous ethanol solutions into components in the region of hydroxyl group stretching vibrations are presented. The infrared light absorption and Raman scattering spectra are investigated for alcohol concentrations in the solution changing from 0 to 90 mass %. Methods of higher derivatives and genetic algorithms together with the simplex method are used to investigate the OH stretching vibrational band contour. Independent methods of spectral structure resolution demonstrate good agreement in the number of the major spectral components as well as in the dependences of the peak wavenumbers, band widths, and amplitudes of spectral components on the ethanol concentration in water. The observed changes in the shape of the spectral contour for OH stretching vibration and, therefore, its components are explained in terms of the hydrogen bonding in non-electrolyte/water mixtures.

Conformational stabilities from variable temperature Raman spectra, r0 structural parameters and vibrational assignments of 1,2-diphosphinoethane

Infrared spectra (3600–500cm−1) of gas, amorphous, crystalline solid and Raman spectra (3000–200cm−1) of liquid and solid were recorded. Variable temperature Raman spectra (30 to −38°C) of liquid were recorded which indicates the presence of significant amounts of six conformers at ambient temperature. Rotation about CC bond gives Trans (T) and Gauche (G) conformers and rotation around both CP bonds gives trans (t) and gauche (g) forms. Enthalpy differences for five of the lower energy conformers w.r.t. the lowest energy tTt form were determined to be 272±39cm−1, 434±40cm−1, 443±30cm−1, 663±60cm−1 and 671±34cm−1 for g′Tt, g′Tg′, g′Tg, tG′g′ and tG′t conformers, respectively, which are in the increasing order of energy. Ab initio calculations with various basis sets up to aug-cc-pVTZ were performed and to support the spectroscopic studies MP2(full)/6-31G(d) was used to predict Raman activities, infrared intensities, vibrational frequencies and band contours. By utilizing the previously reported microwave rotational constants along with MP2(full)/6-311+G(d,p) predictions, adjusted r0 parameters were obtained for two Trans and two Gauche (CC bond) conformers. The determined heavy atom structural parameters for g′Tt [g′Tg′] {tG′g′} |tG′t| conformers are: distances (Å) P1C2=1.870(3) [1.866(3)] {1.858(3)} |1.859(3)|, C2C3=1.535(3) [1.536(3)] {1.534(3)} |1.536(3)|, C3P4=1.863(3) [1.866(3)] {1.866(3)} |1.859(3)|, and angles (°) ∠P1C2C3=110.5(5) [110.4(5)] {117.0(5)} |118.5(5)|, ∠C2C3P4=115.5(5) [110.4(5)] {113.7(5)} |118.5(5)|. The results are discussed and compared to the corresponding properties of some similar molecules.

Car–Parrinello Simulation of the Vibrational Spectrum of a Medium Strong Hydrogen Bond by Two-Dimensional Quantization of the Nuclear Motion: Application to 2-Hydroxy-5-nitrobenzamide

The nature of medium strong intra- and intermolecular hydrogen bonding in 2-hydroxy-5-nitrobenzamide in the crystal phase was examined by infrared spectroscopy and Car-Parrinello molecular dynamics simulation. The focal point of our study was the part of the infrared spectra associated with the O-H and N-H stretching modes that are very sensitive to the strength of hydrogen bonding. For spectra calculations we used an isolated dimer and the fully periodic crystal environment. We calculated the spectra by using harmonic approximation, the time course of the dipole moment function as obtained from the Car-Parrinello simulation, and the quantization of the nuclear motion of the proton for an instantaneous snapshot of the structures in one and two dimensions. Although quantitative assessment of the agreement between the computed and experimental band contour is difficult due to the fact that the experimental band is very broad, we feel that the most reasonable qualitative agreement with the experiment is obtained from snapshot structures and two-dimensional quantization of the proton motion. We have also critically examined the methods of constructing the one-dimensional proton potential. Perspectives are given for the treatment of nuclear quantum effects in biocatalysis.

Two-dimensional laser induced fluorescence spectroscopy of van der Waals complexes: Fluorobenzene-Arn (n = 1,2)

The technique of two-dimensional laser induced fluorescence (2D-LIF) spectroscopy has been used to observe the van der Waals complexes fluorobenzene-Ar and fluorobenzene-Ar(2) in the region of their S(1)-S(0) electronic origins. The 2D-LIF spectral images reveal a number of features assigned to the van der Waals vibrations in S(0) and S(1). An advantage of 2D-LIF spectroscopy is that the LIF spectrum associated with a particular species may be extracted from an image. This is illustrated for fluorobenzene-Ar. The S(1) van der Waals modes observed in this spectrum are consistent with previous observations using mass resolved resonance enhanced multiphoton ionisation techniques. For S(0), the two bending modes previously observed using a Raman technique were observed along with three new levels. These agree exceptionally well with ab initio calculations. The Fermi resonance between the stretch and bend overtone has been analysed in both the S(0) and S(1) states, revealing that the coupling is stronger in S(0) than in S(1). For fluorobenzene-Ar(2) the 2D-LIF spectral image reveals the S(0) symmetric stretch van der Waals vibration to be 35.0 cm(-1), closely matching the value predicted based on the fluorobenzene-Ar van der Waals stretch frequency. Rotational band contour analysis has been performed on the fluorobenzene-Ar 0(0)(0) transition to yield a set of S(1) rotational constants A' = 0.05871 ± 0.00014 cm(-1), B' = 0.03803 ± 0.00010 cm(-1), and C' = 0.03103 ± 0.00003 cm(-1). The rotational constants imply that in the S(1) 0(0) level the Ar is on average 3.488 Å from the fluorobenzene centre of mass and displaced from it towards the centre of the ring at an angle of ~6° to the normal. The rotational contour for fluorobenzene-Ar(2) was predicted using rotational constants calculated on the basis of the fluorobenzene-Ar geometry and compared with the experimental contour. The comparison is poor which, while due in part to expected saturation effects, suggests the presence of another band lying beneath the contour.

Amine inversion effects on the IR spectra of aniline in the gas phase and cold inert gas matrixes

The mid-infrared spectrum of aniline vapour is reinvestigated, and the IR spectrum of the compound in solid nitrogen matrix under a cryogenic condition is measured for the first time. A thorough assignment of many features of the vapour spectrum, particularly those related to amine inversion mode, is suggested. By use of PGOPHER fitting of the rotational band contours in the fingerprint region, the amine inversion tunnelling splitting at v = 1 level of NH2 scissoring and C–N bending vibrations in the vapour spectrum are identified. Our analysis reveals that excitation of one quantum of NH2 scissoring results in lowering of the tunnelling barrier, whereas, the barrier is increased upon excitation of the C–N bending. Comparison of the spectra recorded in nitrogen and argon matrixes reveal that the former hinders the NH2 inversion and consequently, transitions corresponding to higher quanta of this mode are absent.

Microwave, infrared and Raman spectra, r structural parameters, ab initio calculations and vibrational assignment of 1-fluoro-1-silacyclopentane

The microwave spectrum (6500-18 ,500 MHz) of 1-fluoro-1-silacyclopentane, c-C(4)H(8)SiHF has been recorded and 87 transitions for the (28)Si, (29)Si, (30)Si, and (13)C isotopomers have been assigned for a single conformer. Infrared spectra (3050-350 cm(-1)) of the gas and solid and Raman spectrum (3100-40 cm(-1)) of the liquid have also been recorded. The vibrational data indicate the presence of a single conformer with no symmetry which is consistent with the twist form. Ab initio calculations with a variety of basis sets up to MP2(full)/aug-cc-pVTZ predict the envelope-axial and envelope-equatorial conformers to be saddle points with nearly the same energies but much lower energy than the planar conformer. By utilizing the microwave rotational constants for seven isotopomers ((28)Si, (29)Si, (30)Si, and four (13)C) combined with the structural parameters predicted from the MP2(full)/6-311+G(d,p) calculations, adjusted r(0) structural parameters have been obtained for the twist conformer. The heavy atom distances in Å are: r(0)(SiC(2)) = 1.875(3); r(0)(SiC(3)) = 1.872(3); r(0)(C(2)C(4)) = 1.549(3); r(0)(C(3)C(5)) = 1.547(3); r(0)(C(4)C(5)) = 1.542(3); r(0)(SiF) = 1.598(3) and the angles in degrees are: [angle]CSiC = 96.7(5); [angle]SiC(2)C(4) = 103.6(5); [angle]SiC(3)C(5) = 102.9(5); [angle]C(2)C(4)C(5) = 108.4(5); [angle]C(3)C(5)C(4) = 108.1(5); [angle]F(6)Si(1)C(2) = 110.7(5); [angle]F(6)Si(1)C(3) = 111.6(5). The heavy atom ring parameters are compared to the corresponding r(s) parameters. Normal coordinate calculations with scaled force constants from MP2(full)/6-31G(d) calculations were carried out to predict the fundamental vibrational frequencies, infrared intensities, Raman activities, depolarization values, and infrared band contours. These experimental and theoretical results are compared to the corresponding quantities of some other five-membered rings.