ATR-far-ultraviolet spectroscopy: a challenge to new σ chemistry.

This review reports the recent progress on ATR-far ultraviolet (FUV) spectroscopy in the condensed phase. ATR-FUV spectroscopy for liquids and solids enables one to explore various topics in physical chemistry, analytical chemistry, nanoscience and technology, materials science, electrochemistry, and organic chemistry. In this review, we put particular emphasis on the three major topics: (1) studies on electronic transitions and structures of various molecules, which one cannot investigate via ordinary UV spectroscopy. The combined use of ATR-FUV spectroscopy and quantum chemical calculations allows for the investigation of various electronic transitions, including σ, n-Rydberg transitions. ATR-FUV spectroscopy may open a new avenue for σ-chemistry. (2) ATR-FUV spectroscopy enables one to measure the first electronic transition of water at approximately 160 nm without peak saturation. Using this band, one can study the electronic structure of water, aqueous solutions, and adsorbed water. (3) ATR-FUV spectroscopy has its own advantages of the ATR method as a surface analysis method. ATR-FUV spectroscopy is a powerful technique for exploring a variety of top surface phenomena (∼50 nm) in adsorbed water, polymers, graphene, organic materials, ionic liquids, and so on. This review briefly describes the principles, characteristics, and instrumentation of ATR-FUV spectroscopy. Next, a detailed description about quantum chemical calculation methods for FUV and UV regions is given. The recent application of ATR-FUV-UV spectroscopy studies on electronic transitions from σ orbitals in various saturated molecules is introduced first, followed by a discussion on the applications of ATR-FUV spectroscopy to studies on water, aqueous solutions, and adsorbed water. Applications of ATR-FUV spectroscopy in the analysis of other materials such as polymers, ionic liquids, inorganic semiconductors, graphene, and carbon nanocomposites are elucidated. In addition, ATR-FUV-UV-vis spectroscopy focusing on electrochemical interfaces is outlined. Finally, FUV-UV-surface plasmon resonance studies are discussed.

Observation of Solid-Liquid Phase Transitions of Brine Using the Far-Ultraviolet Charge-Transfer-to-Solvent Band.

Although determining the chemical states of salts and ions is critical in numerous fields, such as elucidating biological functions and maintaining food quality, the current direct observation methods are insufficient. We propose a spectral analysis method of directly observing the phase transitions of NaCl solutions using the changes in the charge-transfer-to-solvent band and the absorption band representing the first electron transition (à ← X̃) of H2O. The intensities of these bands may be observed using attenuated total reflection far-ultraviolet spectroscopy. According to the well-known phase diagram of aqueous NaCl, we observe spectral changes during freezing-thawing and may spectroscopically detect the phase transitions from liquid to mixed liquid-solid and solid phases, including eutectic crystals, in addition to their coexistence curves.

A Study of C=O HO and OH OH (Dimer, Trimer, and Oligomer) Hydrogen Bonding in a Poly(4-vinylphenol) 30%/Poly(methyl methacrylate) 70% Blend and its Thermal Behavior Using Near-Infrared Spectroscopy and Infrared Spectroscopy.

Inter- and intramolecular hydrogen bonding and their temperature-dependent changes in a poly(4-vinylphenol)/poly(methyl methacrylate)(PVPh 30%/PMMA 70%) blend were investigated using near-infrared (NIR) and infrared (IR) spectroscopy. Band assignments of the fundamentals and first overtones of the OH stretching mode of a free OH group and OH groups in C=O···HO and OH···OH (dimer, trimer, and oligomer) hydrogen bonding of PVPh 30%/PMMA 70% were carried out by comparison between its NIR and IR spectra and comparison with NIR and IR spectra of phenol. The comparison of the NIR spectra of the PVPh 30%/PMMA 70% blend (hereafter, we denote it as PVPh30%) with the corresponding IR spectra reveals that to observe bands arising from the free OH and OH···OH dimer, which is a weaker hydrogen bonding, NIR is better while to investigate bands originating from OH groups in the OH···O=C and OH···OH (oligomer) hydrogen bonds, which are stronger hydrogen bonding, IR is better. Thus, a combination of IR and NIR spectroscopy has provided convincing results for the hydrogen bonding of PVPh30%. The relative intensity of the two bands at 7058 and 6921 cm-1 (I7058/I6921) due to the first overtones of the OH stretching modes of the free OH group and the OH group in the dimer, respectively, increases significantly above 90 °C, which is close to Tg of PVPh. In concomitance with the intensity increase in the relative intensity of the free OH band, the intensity of a band at 1706 cm-1 due to the C=O stretching mode of the C=O···HO hydrogen bond of PVPh30% decreases above 90°C. These results suggest that above the Tg of PVPh the C=O···HO hydrogen bond is broken gradually and that the free OH increases. Of note is that below Tg the intensities of NIR bands due to the OH first overtones of free OH group and OH groups in the OH···OH dimer gain intensity in parallel with temperature increase, and above Tg the intensity of the band derived from the OH···OH group increases linearly much slower than that of the band due to the free OH. Moreover, a band due to an OH···OH oligomer decreases linearly. Hence, it is very likely that the OH···OH oligomers dissociate into free OH groups. Anharmonicity of O-H bonds, which is sensitive to a hydrogen bond, was estimated for the free OH and OH bonds in the C=O···HO and OH···OH (dimer, trimer, and oligomer) hydrogen bonding by comparison between the NIR and IR spectra in the OH stretching band regions.

Experimental verification of increased electronic excitation energy of water in hydrate-melt water by attenuated total reflection-far-ultraviolet spectroscopy.

The demand for Li secondary batteries is increasing, with the need for batteries with a higher level of performance and improved safety features. The use of a highly concentrated aqueous electrolyte solution is an effective way to increase the safety of batteries because it is possible to use "water-in-salt" (WIS) and "hydrate-melt" (HM) electrolytes for practical applications. These electrolytes exhibit a potential window of >3.0 V, which is attributed to the difference between the HOMO and the LUMO energies of the n orbital of the pure water molecules and that of the water molecules in the hydration shells of a metal ion, according to theoretical predictions. Thus, in the present study, the attenuated total reflectance (ATR)-far-ultraviolet (FUV) spectra of water and super-concentrated aqueous solutions, such as WIS and HM using a Li salt, were experimentally investigated. The effects of anions, cations, and deuteriums on the ATR-FUV spectra were examined. The ATR-FUV method is an excellent means of studying highly concentrated aqueous salt solutions. The results suggest that the transition energy of water molecules in an ultrahighly concentrated aqueous electrolyte containing HM and WIS increased by nearly 0.4 eV (corresponding to an energy shift of over 10 nm) compared to an aqueous electrolyte with a typical water concentration. It was also revealed that the transition energy of water changes depending on the environment of the non-bonding electron, which is directly connected with or affected by hydrogen bonding with other water molecules or directly connected with Li+.

Attenuated Total Reflection Far-Ultraviolet (ATR-FUV) Spectroscopy is a Sensitive Tool for Investigation of Protein Adsorption.

Attenuated total reflection far-ultraviolet (ATR-FUV) spectra in the 145-250 nm region were studied for four kinds of proteins (two α-helix-rich proteins: bovine serum albumin (BSA) and lysozyme and two ß-sheet rich proteins: concanavalin A and γ-globulin) in different solutions (pure water and phosphate buffered saline, or PBS) with different concentrations. All the spectra show a band at 191 nm due to the π-π* transition of amide bonds of the proteins. The wavelength of the band does not change with their second structures, suggesting that the corresponding electronic transition mode is localized and polarized in the direction that is not affected by the difference in the peptide folding. The intensity of the 191 nm band differs with the concentration of salt in the solution, suggesting that the band intensity reflects the adsorption density of a protein on the internal reflection element (IRE) made of a sapphire glass prism. According to the intensity changes of the band at 191 nm, it is revealed that the properties in adsorption are different from one protein to another. It is assumed that there are two types of forces on the protein adsorption: one is that among the molecules and the other is that between a molecule and a substrate. The origin of force includes localized electrostatic polarity and affinity to water. The ions in the solvent give a marked effect on these forces, resulting in the difference in the response to adsorption density against the salt concentration in the solvent.

Solvent Effect on Assembling and Interactions in Solutions of Phenol: Infrared Spectroscopic and Density Functional Theory Study.

This work provides new insight into assembling of phenol in various solvents and competition between different kinds of interactions. To examine both weak and strong interactions, we selected a series of non-aromatic and aromatic solvents. Infrared spectra were measured at low (0.05 M) and high (2 M) phenol content. In addition, we performed density functional theory calculations of the structures and harmonic vibrational spectra of 1:1 complexes of phenol with the solvents and the associates of phenol from dimer to tetramer. Based on these results, we divided the solvents into three groups. The first group consists of non-aromatic solvents weakly interacting with phenol. Depending on the concentration, molecules of phenol in these solvents remain non-bonded or self-associated. In diluted solutions of phenol in chlorinated non-aromatic solvents do not appear free OH groups, since they are involved in a weak OH···Cl interaction. It is of note that in diluted solutions of phenol in tetramethyl ethylene both the non-bonded and bonded OH coexists due to solvent-solvent interactions. The second group consists of aromatic solvents with methyl or chlorine substituents. At low concentration, the molecules of phenol are involved in the phenol-solvent OH···π interaction and the strength of these interactions depends on the solvent properties. At a higher phenol content an equilibrium exists between phenol-solvent OH···π and phenol-phenol OH···OH interactions. Finally, the third group includes the aromatic and non-aromatic solvents with highly polar group (C≡N). In these solvents, regardless of the concentration all molecules of phenol are involved in the solute-solvent OH···NC interaction. Comparison of the experimental and theoretical band parameters reveals that molecules of phenol in non-aromatic solvents prefer the cyclic associates, while in the aromatic solvents they tend to form the linear associates.

Far-Ultraviolet Spectroscopy and Quantum Chemical Calculation Studies of the Conformational Dependence on the Electronic Structure and Transitions of Cyclohexane, Methyl and Dimethyl Cyclohexane, and Decalin; Effects of Axial Substitutions on the Electronic Transitions.

Far-ultraviolet (FUV) spectra were measured for cyclohexane, methyl cyclohexane, six isomers of dimethyl cyclohexane, and cis- and trans-decalin. Attenuated total reflection-FUV (ATR-FUV) spectroscopy, which we originally proposed, provides systematic information about the excitation states of saturated organic molecules and the hyperconjugation of σ bonds. The FUV spectra of cyclohexane and methyl cyclohexane in neat liquids showed a band with central wavelengths near 155 and 162 nm. The simulation spectrum of cyclohexane calculated by time-dependent density-functional theory (TD-DFT) (CAM-B3LYP/aug-cc-pVTZ) gives two bands at 146 and 152 nm owing to the transition from HOMO-2 to Rydberg 3pz (Tb) and those from HOMO and HOMO-1 to Rydberg 3px/3py (Ta), respectively. The simulation spectrum of methyl cyclohexane with the equatorial substituent has peaks at approximately the same positions as cyclohexane. The calculated molar absorption coefficient is larger than that of cyclohexane, estimating the observed FUV spectra very well. The FUV spectra of dimethyl cyclohexane with two methyl substituents at the equatorial positions (trans-1,2-, cis-1,3-, and trans-1,4-) and trans-decalin had similar features to those of cyclohexane and methylcyclohexane. The TD-DFT calculations revealed that the shoulders at the shorter- and longer-wavelength sides of the band center of dimethyl cyclohexane (with methyl substituents at equatorial positions) and trans-decalin are assigned to Tb and Ta, respectively. In the case of dimethyl cyclohexane with one methyl substituent in the axial position (cis-1,2-, trans-1,3-, and cis-1,4-) and cis-decalin, the band caused by Tb decreased compared to those of the other compounds. The decrease in intensity and the longer-wavelength shift of the Tb band for dimethyl cyclohexane (with one methyl group at the axial position) and cis-decalin revealed that the band on the longer-wavelength side was assigned to the overlap band of Ta and Tb. The reason for such a large spectral alternation for the axial substitution may be the increase in the orbital energy of HOMO-2, which has its electron density concentrated at the axial C-H bond. Regarding the effect of the hyperconjugation of C-C and C-H σ orbitals, the second perturbation energies of the interaction between Cα-Hax and Cß-Hax were estimated for molecules by natural bond orbital (NBO) analysis. There is a correlation between the orbital energies of HOMO-2 and the changes in vicinal interaction by axial substitution.

Solvent effect on the competition between weak and strong interactions in phenol solutions studied by near-infrared spectroscopy and DFT calculations.

Near-infrared (NIR) spectra of phenol in a series of non-aromatic and aromatic solvents were recorded to study the competition between various types of solute-solute and solute-solvent interactions. Depending on the phenol concentration, the free OH and OH involved in the OH⋯OH interactions in the dimers and higher associates are present in cyclohexane solutions. On the other hand, free OH does not appear in Cl-containing solvents since at a low phenol content the OH groups participate in the OH⋯Cl interactions. In CCl4 and tetrachloroethylene this interaction is weak, while in chlorobenzene the strength of this interaction is higher. In the aromatic solvents the solute-solute OH⋯OH interactions compete with the solute-solvent OH⋯π and aromatic CH⋯OH ones. Consequently, the degree of self-association of phenol in aromatic solvents is smaller than that in non-aromatic ones. The strength of the OH⋯π interactions increases with growing electron-donating ability of the substituents in the benzene derivatives. This observation obtained from the NIR spectra is in line with the results of the theoretical calculations (DFT). A clear correlation appears between the number of methyl groups in aromatic solvents and the population of the free OH groups. The methyl groups are steric hindrances and impede the formation of the OH⋯OH and OH⋯π interactions. Our results suggest the presence of aromatic CH⋯OH solute-solvent interactions, not observed in previous studies. NIR spectroscopy appears to be a powerful tool for exploration of free and weakly-bonded OH groups.

Advances, challenges and perspectives of quantum chemical approaches in molecular spectroscopy of the condensed phase.

The purpose of this review is to demonstrate advances, challenges and perspectives of quantum chemical approaches in molecular spectroscopy of the condensed phase. Molecular spectroscopy, particularly vibrational spectroscopy and electronic spectroscopy, has been used extensively for a wide range of areas of chemical sciences and materials science as well as nano- and biosciences because it provides valuable information about structure, functions, and reactions of molecules. In the meantime, quantum chemical approaches play crucial roles in the spectral analysis. They also yield important knowledge about molecular and electronic structures as well as electronic transitions. The combination of spectroscopic approaches and quantum chemical calculations is a powerful tool for science, in general. Thus, our article, which treats various spectroscopy and quantum chemical approaches, should have strong implications in the wider scientific community. This review covers a wide area of molecular spectroscopy from far-ultraviolet (FUV, 120-200 nm) to far-infrared (FIR, 400-10 cm-1)/terahertz and Raman spectroscopy. As quantum chemical approaches, we introduce several anharmonic approaches such as vibrational self-consistent field (VSCF) and the combination of periodic harmonic calculations with anharmonic corrections based on finite models, grid-based techniques like the Numerov approach, the Cartesian coordinate tensor transfer (CCT) method, Symmetry-Adapted Cluster Configuration-Interaction (SAC-CI), and the ZINDO (Semi-empirical calculations at Zerner's Intermediate Neglect of Differential Overlap). One can use anharmonic approaches and grid-based approaches for both infrared (IR) and near-infrared (NIR) spectroscopy, while CCT methods are employed for Raman, Raman optical activity (ROA), FIR/terahertz and low-frequency Raman spectroscopy. Therefore, this review overviews cross relations between molecular spectroscopy and quantum chemical approaches, and provides various kinds of close-reality advanced spectral simulation for condensed phases.

Attenuated Total Reflection-Far-Ultraviolet Spectroscopy and Quantum Chemical Calculations of the Electronic Structure of the Top Surface and Bulk of Polyethylenes with Different Crystallinities.

In this study, we explored the electronic structure of the surfaces of polyethylene samples having different crystallinities using attenuated total reflection (ATR) far-ultraviolet (FUV) spectroscopy and quantum chemical calculations. Specifically, the ATR-FUV spectra of five types of high-density polyethylene (HDPE), six types of linear low-density PE (LLDPE), and seven types of low-density PE (LDPE) were obtained. All the spectra contained an intense band near 156 nm and a broad band between 180 and 190 nm. Transmission spectra were obtained for the thin-film (30 µm) PE samples between 165 and 250 nm. In this region, the HDPE films show very low-intensity bands. In contrast, the transmission spectra of the LLDPE and LDPE samples yielded weak-to-medium and medium-intensity bands around 180-190 nm, respectively. In addition, to understand the differences in the absorption spectra among the PEs observed, we simulated the spectra of n-pentane as a PE crystal model using time-dependent density functional theory and found that the common intense band at 156 nm is due to the σ (C(2p)-H)→Rydberg 3s, 3p transition. The absorption bands near 180-190 nm may correspond to aggregates of numerous molecular chains in the amorphous parts of the LLDPE and LDPE samples.

ATR-far-ultraviolet spectroscopy in the condensed phase-The present status and future perspectives.

Far-ultraviolet (FUV) spectroscopy in the region of 140-200 nm of condensed-phase has received keen interest as a new electronic spectroscopy. The introduction of the attenuated total reflection (ATR) technique to the FUV region has opened a new avenue for FUV spectroscopy of liquids and solids. ATR-FUV spectroscopy enables the study of electronic structures and transitions of most types of molecules. It also holds great promise for a variety of applications, i.e., from the application to basic sciences to practical applications. In this review, the characteristics and advantages of ATR-FUV spectroscopy in the condensed phase are described first; then, a brief historical overview is provided. Next, the ATR-FUV spectroscopy instrumentation is outlined. After these introductory parts, a variety of AFT-FUV spectroscopy applications are introduced, starting from applications to investigations of electronic structure and transitions of alkanes, graphenes, and polymers. Then, time-resolved ATR-FUV spectroscopy is discussed. The applications to materials research, such as the research on inorganic semiconductors and ionic liquids, follow. In the last part, the FUV spectroscopy perspective is emphasized.

Solvation effects on wavenumbers and absorption intensities of the OH-stretch vibration in phenolic compounds - electrical- and mechanical anharmonicity via a combined DFT/Numerov approach.

Previous measurements of fundamental, first-, second- and third overtones of the OH-stretching vibration of phenol and 2,6-difluoro-phenol by use of visible (Vis), near-infrared (NIR) and infrared (IR) spectroscopy revealed an oscillating pattern in the intensity quotient between the two kinds of solvents, carbon tetrachloride and n-hexane, upon increase of the vibrational quantum number, which could not be reproduced utilizing quantum mechanical calculations in implicit solvation. In the present study this phenomenon was successfully explained for the first time, employing an explicit consideration of solute-solvent interactions in combination with modern grid-based methods to solve the time-independent Schrödinger equation. The capabilities of this framework of (i) not requiring any assumptions on the form of the resulting wave function, (ii) focusing the description on the vibrational mode of interest and (iii) taking solute-solvent interactions explicitly into account are a particularly lucid example of the advantages in applying state-of-the-art approaches in investigations of challenging vibrational quantum problems. The property of grid-based methods being directly applied onto any given potential energy grid together with point (i) enable to analyse the impact of mechanical- and electrical anharmonicity independently. Especially the detailed investigation of the latter contribution when moving from a harmonic to an anharmonic potential in conjunction with the explicit consideration of solvent effects at the example of an actual chemical system (i.e. not discussing these effects employing mere model potentials) demonstrate the manifold benefit achieved using the applied DFT/Numerov strategy.

Surface Structural Transformation of Pre-carbonized Solid Biomass from Japanese Cedar via ATR-FTIR and PCA.

This present research applied the ATR-FTIR technique and principle component analysis (PCA) to investigate molecular surface changes in pre-carbonized solid biomass, called Kindai Bio-coke (BIC) and Japanese cedar. The product is utilized as an alternative to coal coke in the cupola furnace in the steel industry in order to reduce CO2 emissions. The aim is to explore key elements for improving the BIC product applications from the fundamental molecular scale by using PCA to distinguish between changes during the BIC transformation and the differences in BIC samples. Results revealed that transformation occurred at the surface of Japanese cedar raw materials and Japanese cedar BIC. Major changes were observed in the O-H, C-H and C-O stretching regions. The intensity of the IR bands attributed to aliphatic methyl (CH3) and methylene (CH2) stretching modes increased, while a weak O-H stretching intensity associated with BIC hydrophobic characteristic decreased.

Determining the Coordination Number of Li+ and Glyme or Poly(ethylene glycol) in Solution Using Attenuated Total Reflectance-Far Ultraviolet Spectroscopy.

Attenuated total reflectance-far ultraviolet (ATR-FUV) spectra of Li+ and polyether ligands, such as glymes and poly (ethylene glycol) (PEG), in solution give information about changes in the electronic states of the ligands. From the ATR-FUV spectra, the coordination numbers between Li+ and monoglyme, diglyme, triglyme, and PEG400 were determined to be 4, 5, 6, and 5, respectively. Our results indicate that Li+ is coordinated only by the ligands rather than its counter-ions.

Changes in the Electronic Transitions of Polyethylene Glycol upon the Formation of a Coordinate Bond with Li+, Studied by ATR Far-Ultraviolet Spectroscopy.

This study investigates the electronic transitions of complexes of lithium with polyethylene glycol (PEG) by the absorption bands of solvent molecules via attenuated total reflectance spectroscopy in the far-UV region (ATR-FUV). Alkali-metal complexes are interesting materials because of their functional characteristics such as good ionic conductivity. These complexes are used as polymer electrolytes for Li batteries and as one of the new types of room-temperature ionic liquids, termed solvation ionic liquids. Considering these applications, alkali-metal complexes have been studied mainly for their electrochemical characteristics; there is no fundamental study providing a clear understanding of electronic states in terms of electronic structures for the ground and excitation states near the highest occupied molecular orbital-lowest occupied molecular orbital transitions. This study explores the electronic transitions of ligand molecules in alkali-metal complexes. In the ATR-FUV spectra of the Li-PEG complex, a decrease in intensity and a large blue shift (over 4 nm) were observed to result from an increase in the concentration of Li salts. This observation suggests the formation of a complex, with coordinate bonding between Li+ and the O atoms in PEG. Comparison of the experimental spectrum with a simulated spectrum of the Li-PEG complex calculated by time-dependent density functional theory indicated that changes in the intensities and peak positions of bands at approximately 155 and 177 nm (pure PEG shows bands at 155, 163, and 177 nm) are due to the formation of coordinate bonding between Li+ and the O atoms in the ether molecule. The intensity of the 177 nm band depends on the number of residual free O atoms in the ether, and the peak wavelength at approximately 177 nm changes with the expansion of the electron clouds of PEG. We assign a band in the 145-155 nm region to the alkali-metal complex because we observed a new band at approximately 150 nm in the ATR-FUV spectra of very highly concentrated binary mixtures.

Rydberg transitions as a probe for structural changes and phase transition at polymer surfaces: an ATR-FUV-DUV and quantum chemical study of poly(3-hydroxybutyrate) and its nanocomposite with graphene.

We investigated the surface (<50 nm) of poly(3-hydroxybutyrate) (PHB) and its nanocomposite with graphene by attenuated total reflection far- and deep-ultraviolet (ATR-FUV-DUV; 145-300 nm; 8.55-4.13 eV) spectroscopy and quantum mechanical calculations. The major absorption of polymers occurs in FUV and is related to Rydberg transitions. ATR-FUV-DUV spectroscopy allows for direct measurements of these transitions in the solid phase. Using ATR-FUV-DUV spectroscopy, periodic density functional theory (DFT) and time-dependent DFT (TD-DFT), we explained the origins of the FUV-DUV absorption of PHB and provided insights into structural changes of PHB which occur upon formation of a graphene nanocomposite and upon heating of the pure polymer. The structural changes cause specific and gradual spectral variations in FUV-DUV. We systematically studied the relaxation of the polymer helix and concluded that the common feature of all models of the unfolded helix lies in a specific and consistent FUV-DUV spectral signature. Relaxed structures feature a blue-shift of the major FUV transition (non-bonding molecular orbital to Rydberg 3p and π to π*) as compared with crystalline PHB. The FUV absorption of the relaxed structures was determined to be significantly stronger than that of the crystalline state. These results are consistent with the observed temperature-dependent spectra of the pure PHB. The simulation of the thermal expansion of the crystalline polymer by a periodic-DFT study allows us to exclude the possibility that spectral variations observed experimentally are influenced by changes in the crystalline phase. We concluded that the crystallinity of PHB at the sample surface increases with an increase in graphene content in the nanocomposite. However, it is unlikely that the polymer structure inside the crystal is affected; instead the FUV-DUV spectral variations result from changes in the polymer morphology that occur at the sample surface. The phase transition of PHB is affected by temperature and addition of graphene content. These changes are likely to be the opposite of those occurring in the bulk sample.

Elucidation of the electronic states in polyethylene glycol by attenuated Total reflectance spectroscopy in the far-ultraviolet region.

We measured the attenuated total reflectance-far ultraviolet (ATR-FUV) spectra of poly(ethylene glycol) (PEG; average molecular weights of 200, 300, and 400) and related materials in the liquid state in the 145-200-nm wavelength region. For appropriately assigning the absorption bands, we also performed theoretical simulation of the unit-number dependent electronic spectra. The FUV spectra of PEGs contain three bands, which are assigned to the transitions between n(CH2OCH2)-3s Rydberg state (176 nm), n(CH2OCH2)-3p Rydberg state (163 nm), and n(OH)-3p Rydberg state (153 nm). Since the contribution of n(OH) decreases compared to n(CH2OCH2) with increase in the number of units, the ratios of the molar absorption coefficients, ε, at 153 nm relative to 163 nm, decrease. On the other hand, the ratio of ε at 176 nm to that at 163 nm increases with increase in the number of units, because of the difference in the number of unoccupied orbitals in the transitions. The calculated results suggest that n orbitals form two electronic bands. In the upper band, the electrons expand over the ether chain, whereas in the lower band, the electrons are localized in the terminal OH in the PEGs.

Effects of intermolecular interactions on absorption intensities of the fundamental and the first, second, and third overtones of OH stretching vibrations of methanol and t-butanol­d9 in n-hexane studied by visible/near-infrared/infrared spectroscopy.

Visible (Vis), near-infrared (NIR) and IR spectra in the 15,600-2500cm-1 region were measured for methanol, methanol-d3, and t-butanol-d9 in n-hexane to investigate effects of intermolecular interaction on absorption intensities of the fundamental and the first, second, and third overtones of their OH stretching vibrations. The relative area intensities of OH stretching bands of free and hydrogen-bonded species were plotted versus the vibrational quantum number using logarithm plots (V=1-4) for 0.5M methanol, 0.5M methanol­d3, and 0.5M t-butanol-d9 in n-hexane. In the logarithm plots the relative intensities of free species yield a linear dependence irrespective of the solutes while those of hydrogen-bonded species deviate significantly from the linearity. The observed results suggest that the modifications in dipole moment functions of the OH bond induced by the formation of the hydrogen bondings change transient dipole moment, leading to the deviations of the dependences of relative absorption intensities on the vibrational quantum number from the linearity.

A Correction Method for Attenuated Total Reflection-Far Ultraviolet Spectra Via the Use of Charge Transfer to Solvent Band Intensities of Iodide in the Ultraviolet Region.

Attenuated total reflection (ATR) spectra, which are often used in IR analysis, can be transformed into extinction and refraction spectra by Kramers-Kronig transformation (KKT) with Fresnel equations. However, it is often difficult to obtain correct optical indices due to the inherent instrumental functions. This paper proposes a simple practical method for correction of KKT with two parameters, which include all the effects of the instrumental function. In order to obtain the parameters of the instrumental function, absorption ratios of charge transfer to solvent (CTTS) transitions of aqueous iodide ions observed at 195 nm and 230 nm were used as a standard. The absorption indices calculated from the ATR spectra with the parameters correspond reasonably well to those given by the transmittance spectra not only in the UV region but also in the far-ultraviolet (FUV, 120-200 nm) region. By applying the corrected KKT to the ATR-FUV spectra of aqueous potassium halide solutions in the range of 0-2 M, correct features of the absorption spectra of KCl and KBr, whose CTTS bands are thought to be observed in FUV region, were confirmed. It is possible to use the parameters representing the instrument function as long as the instrument is not changed.