Evans Holes Research Articles

Vibrational spectra, linear and nonlinear optical investigations on 3‑chloro 4-fluoro aniline and 2-iodo aniline for optical limiting applications

Detailed investigations on the linear and nonlinear optical properties of 3‑chloro 4-fluoro aniline (CFA) and 2-iodo aniline (IA) have been carried out to understand their applicability. Natural Bond Orbital (NBO) analysis reveals the potential nonlinearity of CFA and IA by virtue of their π-conjugations in the carbon-ring systems and the n→σ* and n→π* hyperconjugations. Vibrational spectra of the molecules, investigated using the FT-IR and FT-Raman analyses, manifest the incidence of Fermi interaction and Evans hole in IA. The UV–vis spectral analysis brings out the fine photo response of CFA and IA in the visible region.The optical absorption technique has been employed to analyze the optical band gap of the title crystals, through the investigation of the absorption edge, to assess their effectiveness in optical devices.The z-scan measurement brings to light the remarkable third order nonlinearity in IA, with an extraordinary drop in normalized transmittance down to 39% at high laser fluences, which is a clear sign of its potential use as an optical limiter. A study of the molecular docking postures of CFA and IA ligands binding at the active sites of the target proteins reveal them suitable for use as therapeutic agents having anti-inflammation and anti-cancer activities against target proteins.

Effect of resonance dipole-dipole interaction on the infrared spectra of adsorbed CF4. Experimental investigation and theoretical modeling

Adsorption of CF4 on ZnO has been studied by means of FTIR spectroscopy at 55–300K. The contour of the band of the ν3 vibration in the spectra obtained is shown to depend crucially on surface coverage, due to strong resonance dipole-dipole interaction in the layer of adsorbed molecules. At high surface coverage the band is split into two components at 1320 and 1245cm−1, about 75cm−1 apart. The shape of the low frequency component is complicated by an “Evans hole” at 1258cm−1. At lowest coverage only a weak band of ν3 vibration was seen at 1270–1272cm−1; about 10cm−1 below the corresponding wavenumber for gaseous CF4. Preliminary adsorption of CO does not affect significantly the spectrum of adsorbed CF4, leading only to slight decrease of the distance between the two components. Experimentally observed band contours were compared with those calculated theoretically using a model developed earlier for the spectra of interacting molecules in liquid phase, or dissolved in liquefied noble gases, and updated for the case of 2D systems. The calculated spectra reproduce well the splitting of the ν3 band for a monolayer, as well as the coverage and temperature dependence of the IR spectra.

Effect of oxygen impurity on the efficiency of the formation of complexes with H-bond and aggregation of color centers in lithium fluoride

The effect of impurities on the efficiency of the formation of color centers and hydrogen-bonded molecular complexes upon exposure to various radiations in lithium fluoride crystals grown in air is studied. The results of experiments for measuring optical properties, IR vibrational spectra, luminescence, and thermally stimulated luminescence are presented. The fact that the band in the range of 1800–2300 cm–1 corresponds to stretching vibrations of a complex with strong hydrogen bond is proved based on the Fermi-resonance perturbation in the region of 2080 cm–1, shaped as the Evans hole and bands A, B, and C. It is shown that the composition of these complexes includes an OH– ion and an HF molecule. The crucial role of O2‒ V + oxygen dipoles in the aggregation efficiency and gradient distribution of color centers and radiation resistance of hydroxyl ions is revealed. It is shown that products of radiation decomposition of OH– ions stimulate, while decay of O2‒ V + dipoles suppress, the formation of positively charged color centers.

Spectroscopic and non-linear optical studies of two novel optical limiters from dichloroaniline family crystals: 3,4-Dichloroaniline and 3,5-dichloroaniline

Two organic crystals of the isomeric forms of dichloroanilines such as 3, 4-dichloroaniline (3,4-DCA) and 3, 5-dichloroaniline (3,5-DCA) were grown by slow evaporation method and characterized by various analytical techniques. The vibrational normal modes of the samples were theoretically predicted using the scaled quantum mechanical force field procedures with the DFT level calculation and the potential energy distributions of the individual modes were estimated using the normal coordinate analysis. Fermi doublets and Evans holes were identified in the vibrational spectra of samples. The nuclear relaxation contribution to the vibrational polarizabilities and hyperpolarizabilities for the normal modes of the molecules were quantitatively estimated using the DFT method. The results of the calculated NLO responses showed that the vibrational mean contributions to the static polarizabilities and hyperpolarizabilities were smaller than the corresponding electronic contributions for the molecules. The Kurtz and Perry powder SHG efficiencies were measured and both samples have generated the second-harmonics of the fundamentals. The open-aperture Z-scan study results proposed the superior optical limiting property of 3,5-DCA with respect to 3,4-DCA.

Fermi resonance of molecular complexes with strong hydrogen bond in irradiated LiF:OH crystals

Evidence for the formation of molecular complexes with strong hydrogen bond with fluorine in lithium fluoride crystals containing impurities of OH̄ ions and magnesium under the action of irradiation are presented. The proofs are based on Fermi resonance perturbation of IR stretching vibration bands in the region of 1800–2300cm−1. It is established for the first time that the profile of the stretching vibration bands has three types of perturbations owing to Fermi resonance of stretching vibrations with its overtones: (1) the effect on the band profile without perturbation; (2) “Evans hole” at 2080cm−1; (3) A, B, C bands. Manifestation of these particularities depends on a dose and conditions of a crystal irradiation. It is shown that the IR spectra recorded at a helium temperature confirm that the centers with bands at 1800–2300cm−1 belong to the complexes with hydrogen bond. It is proposed that the OH̄ ion, HF molecule and fluorine ion to be considered as the main structural units of the complex.

Spectroscopic studies of the 1:1 complex of piperidine-4-carboxylic acid (isonipecotic acid) with 2,6-dichloro-4-nitrophenol

The 1:1 complex of piperidine-4-carboxylic acid (isonipecotic acid, P4C) with 2,6-dichloro-4-nitrophenol (DCNP), has been investigated by single-crystal X-ray analysis, Raman and FTIR spectroscopy and theoretical calculations. The hydrogen-bonded-ion-pair complex is observed in the crystalline state with the O⋯H⋯OOC hydrogen bond of 2.453(16) Å. FTIR spectrum shows a broad absorption in the 1600–400cm−1 region characteristic of very short OHO hydrogen bond, broken by the Evans holes. The complexes are joined through NH⋯O into a H-bonding network. The NH⋯O mode appears as a broad band in the range of 3100–2000cm−1. In the structure optimized at the B3LYP/6–311++G(d,p) level of theory the proton is transferred from DCNP to P4C, and molecules are joined through the O⋯HOOC hydrogen bond of 2.640Å. The experimental and theoretical infrared spectra are discussed. Detail interpretation of the vibrational spectra has been carried out with the use of computed Potential Energy Distribution (PED).

Evans hole and non linear optical activity in Bis(melaminium) sulphate dihydrate: A vibrational spectral study

Bis(melaminium) sulphate dihydrate (BMSD), an interesting melaminium derivative for nonlinear optical activity, has been subjected to vibrational spectral analysis using FT IR and FT Raman spectra. The analysis has been aided by the Potential Energy Distribution (PED) of vibrational spectral bands, derived using density functional theory (DFT) at B3LYP/6-31G(d) level. The geometry is found to correlate well with the XRD structure and the band profiles for certain vibrations in the finger print region have been theoretically explained using Evans hole. The detailed Natural Bond Orbital (NBO) analysis of the hydrogen bonding in BMSD has also been carried out to understand the correlation between the stabilization energy of hyperconjugation of the lone pair of donor with the σ∗ orbital of hydrogen-acceptor bond and the strength of hydrogen bond. The theoretical calculation shows that BMSD has NLO efficiency, 2.66times that of urea. The frontier molecular orbital analysis points to a charge transfer, which contributes to NLO activity, through N–H…O intermolecular hydrogen bonding between the melaminium ring and the sulphate. The molecular electrostatic potential (MEP) mapping has also been performed for the detailed analysis of the mutual interactions between melaminium ring and sulphate ion.

Evans hole in internal modes IR spectrum of [formula omitted] ions in (NH4)3WO3F3 crystal

Infrared absorption of (NH4)3WO3F3 compound has been studied. Profile of asymmetric band in 600–1000cm−1 range associated with polar W–O vibrations of WO3F33- ions is explicable on the basis of multi-oscillatory dynamics with account of damping. Complex profile with Evans holes proves that internal modes of WO3F33- anions in the fluorine–oxygen octahedron interact due to the effects of the local field.

The dielectric model function: An evidence for the ν3(SO 42−) phonon mixing in gypsum using polarized IR specular reflectance spectroscopy

A complete investigation of the phonon mixing in the ν 3(SO 4 2−) frequency region was made, under experimental geometry where the reflecting crystal plane and the plane of incidence contain two principal dielectric axes. It was shown that although it is monoclinic, in the frequency region under inspection, gypsum could be treated as an orthorhombic crystal. More sophisticated model dielectric functions were introduced for the explanation of the Evans holes in the reflectance spectra. Using the model dielectric function, an appearance of the shoulder at the higher frequency part of the reflectance band was explained in terms of longitudinal and quasilongitudinal phonons. A possibility for Evans type interaction was encountered between the ν 3(SO 4 2−) A u symmetry type mode and probably some of the combination modes.

On the interrelation between frequencies of stretching and bending vibrations in liquid water

The problem is investigated whether the distributions of bending frequencies P( ν bend, T) of H 2O molecules in the liquid could be calculated from statistical distributions P( ν OH, T) of stretching frequencies on the basis of the empirical correlation established for their mean values. It is found that correlations of different kinds fail to reproduce real spectra. They result in a bending band that is too narrow and give rise to an Evans hole in the stretching band. This provides evidence of the strong intermolecular coupling of bending modes, which makes their frequencies statistically independent from stretching frequencies.

Low-temperature (120 K) structure and vibrational spectrum of protonated proton sponge: the adduct of 1,8-bis(dimethylamino)naphthalene (DMAN) with 4,5- dicyanoimidazole (DCI)

Low-temperature (120 K) studies of the structure of the DMAN·DCI adduct indicate that in symmetrical [NHN]+ hydrogen bridge of 2.571 (1) Å length (2.579(2) Å at room temperature) there is a disorder of the H-atom occupying two positions at nitrogen atoms with a distance of 0.94(3) Å. The comparison with the situation at room temperature seems to show a very low barrier for the proton transfer. The low-frequency vibrations with the participation of the whole N(CH3)2 groups observed in Raman and inelastic incoherent neutron scattering (IINS) spectra of about 100 cm−1 excited at room temperature cause the fundamental level of the protonic mode to penetrate or exceed the barrier. The bending CNC vibrations of about 500 cm−1 are strongly coupled with the protonic mode leading to Evans holes in the band ascribed to the 0+ → 0− transition. This hypothesis is consistent with the literature data relating to theoretical studies on H3NHNH3 +, which show that the barrier for the proton transfer disappears at the hydrogen bond length of about 2.55 Å. Copyright © 1999 John Wiley & Sons, Ltd.

Origin of Evans holes in the infrared spectra of strongly hydrogen-bonded complexes. Pyridine—acid systems

IR and Raman studies and normal coordinate treatment of the complexes with strong, close to quasi-symmetrical H-bonds, formed by pyridine and related molecules with acids, have been carried out to elucidate the origin of Evans holes in IR spectra. It has been found that the holes appear near frequencies of those pyridine ring modes that involve the internal ring coordinates coupled kinematically with the proton stretching coordinate. When the H-bonding is so strong that the νXH frequency becomes close to the frequency of such a ring mode, resonance repulsion of frequencies arise, causing the formation of the hole.

Infrared and Raman study of polyaniline Part I. Hydrogen bonding and electronic mobility in emeraldine salts

Infrared and Raman spectra of chemically prepared (doped) protonated forms of polyaniline and its deuterated ND and —C 6D 4—derivatives have been examined. Broad infrared absorption centered near 1100 cm −1 and cut by numerous Evans holes has been observed and interpreted as an NH stretching band of a strong asymmetric interchain NH + ⋯ N hydrogen bond (d N-N ≈ 2.5 Å). Evans holes, which have corresponding Raman bands, have been assigned to various benzenic and semiquinoidal vibrations. A model of highly conducting polyaniline taking into account the proton transfer is proposed and discussed. The inversion of the NH + ⋯ N hydrogen bond leads to interchain conversions which can generate charge carriers.

35Cl nuclear quadrupole resonance and infrared spectroscopic studies of hydrogen bonding in complexes of trichloroacetic acid with various nitrogen and oxygen bases

The 35Cl n.q.r. spectra of 29 trichloroacetic acid complexes with various bases, mainly pyridines and their N-oxides, have been studied. The dependence of the average 35Cl n.q.r. frequencies, text-decoration:overlineνQ, on ΔpKa have been analysed in terms of the proton-transfer equilibrium, and the data can be explained either on the basis of a double-minimum potential function with rapid flipping of the proton between two equilibrium sites or one broad minimum. Infrared spectra of such complexes show very broad absorptions over the whole region, with numerous so-called ‘Evans holes’. Variations of the absorption in complexes from the inversion region are similar to those observed in solution. In solids the range of the inversion is shifted to the lower ΔpKa values. Nitrogen and oxygen bases show similar spectral behaviour. In the vicinity of 50% proton transfer the spectral features are similar for A—H…B and A–…HB+ complexes.

Infrared and raman spectra of crystalline quinuclidin-3-one hemiperchlorate with symmetrical NHN hydrogen bonds

Infrared and Raman studies have been performed on polycrystalline and monocrystalline samples of quinuclidin-3-one hemipercholate which at low temperature contain symmetric [NHN] + hydrogen bonds. The most characteristic feature of the IR spectrum is a continuous broad absorption polarized parallel to the hydrogen bond direction. The Evans holes in the low-frequency range are most probably due to the coupling of protonic vibrations with internal modes of quinuclidine moieties leading to a modulation of the bridge geometry. Unusual isotopic and temperature effects could indicate a particular shape of the potential for the proton motion.

The vibrational spectra of the copper(II) formates: Part III. The vibrations of the water molecules in Cu(HCOO) 2 · 2H 2O

The infrared spectra of Cu(HCOO) 2 · 2H 2O and its deuterated analogues are reported at ambient and liquid nitrogen temperatures. The internal OH modes as well as the librations of the water molecules are discussed and it is shown that the OH and O—D stretching and bending vibrations which have been observed, occur at very low frequencies. This behaviour is explained in terms of the existence of strong hydrogen bonds and also strong copper—water interactions in the crystal. Evans holes are evident in the OH and O—D stretching frequency ranges. The in-plane rocking librations of the water molecules are coupled to the symmetrical OCO bending vibration of the formate groups. The rocking modes and some of the wagging librational modes of the water molecules are positively identified but the twisting modes are only tentatively assigned.

Evans holes in the infrared spectra of some transition metal formate dihydrates

Evans holes have been identified in OH(OD) stretching regions in the ir spectra of M(HCOO)2•2X2O (M = Mn, Co, Ni and Zn; X = H, D) and attributed to Fermi interaction between the stretching mode and an overtone of the bending mode of water.

A classic example of an Evans hole caused by intermolecular interaction in solid 2ND3⋅D2O at 15 to 145 K

The infrared spectra of 2ND3⋅D2O are reported at temperatures between 15 and 140°K. A sharp dip at 2333cm−1 is found to be an Evans hole2−5. The cause of this dip is discussed. (AIP)

35Cl nuclear quadrupole resonance and infrared spectroscopic studies of 2,6-dichloro-4-nitrophenol–amine hydrogen-bonded adducts

The charge distribution in hydrogen bridges of varying strengths in solid 2,6-dichloro-4-nitrophenol complexes has been studied using the n.q.r. technique. The dependence of the average 35Cl n.q.r. frequencies, vn.q.r., on the pKa can be analysed in terms of the proton-transfer equilibrium. vn.q.r. provides evidence for the existence of either a double-minimum potential function or one broad minimum. Infrared spectra of such complexes show very broad absorptions extending to the far-infrared, with numerous so-called ‘Evans holes’ and a weakening or complete disappearance of the protonic stretching vibration band in the usual range above 1800 cm–1.

The structure and ir spectroscopic behaviour of phthalazine hemiperchlorate

X-ray diffraction studies reveal that in phthalazine hemiperchlorate there are short, asymmetric [NH·N] −1, slightly bent hydrogen bonds, the N·N distance being 2.656(16) Å. The anomalous temperature effect in the far infrared absorption is also observed in this case. Numerous Evans holes can be assigned to skeletal distortion modes.