First direct observation of a CO-bridged primary photoproduct of [Ru3(CO)12] by picosecond time-resolved IR spectroscopy

For the first time, a CO-bridged primary photoproduct was observed for [Ru3(CO)12] by using picosecond time-resolved IR spectroscopy (ps-TRIR).     

In-situ study of sol–gel processing by time-resolved infrared spectroscopy

Sol–gel processing of thin films involves time dependent phenomena which are basically driven by solvent evaporation. An example is evaporation induced self-assembly that is used to prepare mesoporous ordered films through self-organization of templating micelles. The possibility to follow in situ as a function of time the evolution of the system can give a better knowledge of the process and the physics and chemistry beneath. Time-resolved infrared techniques have been applied to different sol–gel systems to study time-dependent phenomena, in particular rapid scan time resolved infrared spectroscopy has been used to monitor in situ the process and as a tool to design the sol–gel synthesis.     

Multichannel reaction of C2Cl3 + O2 studied by time-resolved Fourier transform infrared emission spectroscopy

The multichannel reaction of the C(2)Cl(3) radical with O(2) has been studied thoroughly by step-scan time-resolved Fourier transform infrared emission spectroscopy. Vibrationally excited products of Cl(2)CO, CO, and CO(2) are observed and three major reaction channels forming respectively ClCO + Cl(2)CO, CO + CCl(3)O, and CO(2) + CCl(3) are identified. The vibrational state distribution of the product CO is derived from the spectral fitting, and the nascent average vibrational energy of CO is determined to be 59.9 kJ/mol. A surprisal analysis is applied to evaluate the vibrational energy disposal, which reveals that the experimentally measured CO vibrational energy is much more than that predicted by statistical model. Combining previous ab initio calculation results, the nonstatistical dynamics and mechanism are characterized to be barrierless addition-elimination via short-lived reaction intermediates including the peroxy intermediate C(2)Cl(3)OO* and a crucial three-member-ring COO intermediate.     

Gas-phase photodissociation of CH3COCN at 308 nm by time-resolved Fourier-transform infrared emission spectroscopy

By using time-resolved Fourier-transform infrared emission spectroscopy, the fragments of HCN(v = 1, 2) and CO(v = 1-3) are detected in one-photon dissociation of acetyl cyanide (CH(3)COCN) at 308 nm. The S(1)(A(")), (1)(n(O), π(?) (CO)) state at 308 nm has a radiative lifetime of 0.46 ± 0.01 μs, long enough to allow for Ar collisions that induce internal conversion and enhance the fragment yields. The rate constant of Ar collision-induced internal conversion is estimated to be (1-7) × 10(-12) cm(3) molecule(-1) s(-1). The measurements of O(2) dependence exclude the production possibility of these fragments via intersystem crossing. The high-resolution spectra of HCN and CO are analyzed to determine the ro-vibrational energy deposition of 81 ± 7 and 32 ± 3 kJ∕mol, respectively. With the aid of ab initio calculations, a two-body dissociation on the energetic ground state is favored leading to HCN + CH(2)CO, in which the CH(2)CO moiety may further undergo secondary dissociation to release CO. The production of CO(2) in the reaction with O(2) confirms existence of CH(2) and a secondary reaction product of CO. The HNC fragment is identified but cannot be assigned, as restricted to a poor signal-to-noise ratio. Because of insufficient excitation energy at 308 nm, the CN and CH(3) fragments that dominate the dissociation products at 193 nm are not detected.     

A relaxation study of poled nonlinear optical polymers by infrared reflection-absorption spectroscopy

The relaxation of poled nonlinear optical (NLO) chromophores in polymer films was characterized by infrared (i.r.) reflection-absorption spectroscopy. Both a guest-host system and a photocrosslinkable polymer system were investigated. Polymethylmethacrylate doped with either 2-methyl-4-nitroaniline or 4(4′-nitrophenylazo)aniline was studied. The photocrosslinkable polymer system, polyvinylcinnamate doped with 3-cinnamoyloxy-4-[4-(N,N-diethylamino)-2-cinnamoyloxy phenyl azo]nitrobenzene was also investigated. Doped NLO active molecules were aligned using the corona poling technique. i.r. spectra as a function of time were used to monitor the relaxation behavior of the oriented dyes after poling. Relaxation of NLO molecules was followed at various characteristic vibrational frequencies. The relaxation behavior of both systems were found to be consistent with those studied by the second harmonic generation technique.     

Ion chemistry of α-diazoketones. 1. A collissional activation study of 1-diazo-3-phenoxypropan-2-one upon elecgtron impact

The gaseous ionic products of 1-diazo-3-phenoxypropan-2-one upon electron impact show that cyclization reactions, which have counterparts in condensed-phase chemistry, occur in competition with a mass spectral Wolff type rearrangement.     

Structure and photochemical behaviour of 3-azido-acrylophenones: a matrix isolation infrared spectroscopy study

(Z)-3-Azido-3-methoxycarbonyl-2-chloro-acrylophenone (MACBP) has been synthesized, isolated in low temperature argon and xenon matrices and studied by FTIR spectroscopy, complemented by DFT(B3LYP)/6-311++G(d,p) calculations. The molecule was characterized both structurally and spectroscopically, and its photochemistry used to probe the mechanism of photo-induced conversion of 3-azido-acrylophenones into oxazoles. In situ UV irradiation (λ = 235 nm) of matrix-isolated MACBP yielded as primary photoproduct a 2H-azirine, which undergoes subsequent photoisomerization to methyl 4-chloro-5-phenyl-1,3-oxazole-2-carboxylate. In a competitive process, a ketenimine is also formed upon photolysis of MACBP. The reported results indicate that this ketenimine must be formed from the starting 3-azido-acrylophenone via a Curtius type concerted rearrangement.     

Studies of alkoxysilane hydrolysis and condensation by fourier-transform infrared spectroscopy with a cylindrical internal-reflection cell

The relative concentrations of unhydrolyzed and hydrolyzed forms of (3-trimethoxysilyl) propyloctadecyldimethylammonium chloride (SiQAC) were determined in aqueous solutions as functions of pH and time. Subtraction of the concentrations of these two forms of SiQAC from the total concentration of SiQAC was assumed to give the concentration of the “condensed” form of SiQAC irrespective of its extent of oligomerization. The silane, SiQAC, is used to modify a variety of surfaces to impart antimicrobial properties. Knowledge of the speciation of SiQAC is required to understand its effect on the efficiency and durability of such chemically modified surfaces. The cylindrical internal- reflection/FTIR spectroscopy was also used to determine the rate constants for hydrolysis and condensation of monomethoxytrimethylsilane (MTMS) in 10% (v/v) water/acetone medium as a function of hydrogen-ion concentration. The hydrolysis of MTMS was found to be first order in both silane and water concentrations. the condensation of trimethylsilanol to form hexamthyldisiloxane was second order in silanol concentration.     

H2 adsorption on 3d transition metal clusters: a combined infrared spectroscopy and density functional study

The adsorption of H2 on a series of gas-phase transition metal (scandium, vanadium, iron, cobalt, and nickel) clusters containing up to 20 metal atoms is studied using IR-multiple photon dissociation spectroscopy complemented with density functional theory based calculations. Comparison of the experimental and calculated spectra gives information on hydrogen-bonding geometries. The adsorption of H2 is found to be exclusively dissociative on Sc(n)O+, V(n)+, Fe(n)+, and Co(n)+, and both atomic and molecularly chemisorbed hydrogen is present in Ni(n)H(m)+ complexes. It is shown that hydrogen adsorption geometries depend on the elemental composition as well as on the cluster size and that the adsorption sites are different for clusters and extended surfaces. In contrast to what is observed for extended metal surfaces, where hydrogen has a preference for high coordination sites, hydrogen can be both 2- or 3-fold coordinated to cationic metal clusters.     

Matrix merging arrangements for the study protein dynamics by time-resolved step-scan Fourier transform infrared spectroscopy and multivariate curve resolution

In this paper, we propose the construction of merging arrangements for combining the information from various runs as a powerful approach to improve the resolution. The bacteriorhodopsin (bR) photocycle has been chosen in this study as an example dealing with the protein dynamics monitored by means of time-resolved step-scan FT-IR spectroscopy. The possibilities of matrix merging are evaluated and results are compared with those from the analysis of individual and augmented matrices. As a conclusion, this strategy provides excellent results for the analysis of this type of time-resolved FT-IR data.     

Transient structures and kinetics of the ferrioxalate redox reaction studied by time-resolved EXAFS, optical spectroscopy, and DFT

The photoredox reaction transients of ferrioxalate in water have been studied by means of time-resolved EXAFS and ultrafast optical transient spectroscopy. The transient spectra and kinetics have been measured from the femtosecond to millisecond range, and the Fe-O bond lengths of the ferrioxalate redox reaction transients have been determined with 2 ps time resolution and 0.04 A accuracy. These data in conjunction with quantum-chemistry DFT and UHF calculations were used to formulate a mechanism for the Fe(III) to Fe(II) redox reaction where dissociation precedes electron transfer. In addition, radical scavenging experiments support the mechanism proposed.     

Local heterogeneity for a Eu3+-doped glass evidenced by time-resolved fluorescence spectroscopy coupled to scanning near-field optical microscopy

Time-resolved fluorescence spectroscopy (TRFS) was applied to an aluminate glass sample doped with Eu3+ cation as a fluorescent probe of the chemical environment and local symmetry. Conventional far-field experiments revealed the presence of two different phases: an amorphous phase featured by a highly disordered environment surrounding the Eu3+ cation and a more ordered polycrystalline phase that exhibits a significant increase in the Eu3+ fluorescence decay time compared to that of the amorphous phase. Near-field fluorescence spectra and decay kinetics were recorded in the frontier region between the two phases using a home-built scanning near-field optical microscope. SNOM-TRFS experiments confirmed the presence of local heterogeneities in this part of the glass at a sub-micrometric spatial scale. Polycrystalline sites featured an important shear-force interaction with the probing fiber optic tip, a longer fluorescence decay time, and a higher Stark splitting of the 5D0 --> 7FJ (J = 1-4) electronic transitions of the Eu3+ cations.     

Mechanistic study of electrocatalytic oxidation of formic acid at platinum in acidic solution by time-resolved surface-enhanced infrared absorption spectroscopy

Surface-enhanced infrared absorption spectroscopy (SEIRAS) combined with cyclic voltammetry or chronoamperometry has been utilized to examine kinetic and mechanistic aspects of the electrocatalytic oxidation of formic acid on a polycrystalline Pt surface at the molecular scale. Formate is adsorbed on the electrode in a bridge configuration in parallel to the adsorption of linear and bridge CO produced by dehydration of formic acid. A solution-exchange experiment using isotope-labeled formic acids (H(12)COOH and H(13)COOH) reveals that formic acid is oxidized to CO(2) via adsorbed formate and the decomposition (oxidation) of formate to CO(2) is the rate-determining step of the reaction. The adsorption/oxidation of CO and the oxidation/reduction of the electrode surface strongly affect the formic acid oxidation by blocking active sites for formate adsorption and also by retarding the decomposition of adsorbed formate. The interplay of the involved processes also affects the kinetics and complicates the cyclic voltammograms of formic acid oxidation. The complex voltammetric behavior is comprehensively explained at the molecular scale by taking all these effects into account.     

Madeiranes,a New Class of Pentacyclic Triterpenes: D-Friedo-madeir-14-en-3β-ol and -3-one,D:C-Friedomadeir-7-en-3β-ol and -3-one

The pentacyclic triterpenes 1a, b and 2a, b are isolated from extracts of Euphorbia mellifera Arr. Their structures, determined by X-ray analysis, are supported in part by MS, NMR, and IR data. The skeleton differs from that of representatives of the lupane or hopane class by (i) an unusual arrangement of the substituents in the cyclopentane ring E, the Me group being on C(19) and the i-Pr group in an angular position on C(17), and (ii) a cis D/E ring junction. We propose to name Die unknown pentacyclic parent ‘madeirane’, thus 1a, b and 2a, b are D-friedomadeir-14-ene and D:C-friedomadeir-7-ene derivatives. The biosynthesis of these compounds may be rationalized via ‘spirodammaranol’-cation intermediates 5 and 5′ and madeiranol cation 6 , as outlined in Scheme 2.     

Amine-functionalized lanthanide-doped zirconia nanoparticles: optical spectroscopy, time-resolved fluorescence resonance energy transfer biodetection, and targeted imaging

Ultrasmall inorganic oxide nanoparticles doped with trivalent lanthanide ions (Ln(3+)), a new and huge family of luminescent bioprobes, remain nearly untouched. Currently it is a challenge to synthesize biocompatible ultrasmall oxide bioprobes. Herein, we report a new inorganic oxide bioprobe based on sub-5 nm amine-functionalized tetragonal ZrO(2)-Ln(3+) nanoparticles synthesized via a facile solvothermal method and ligand exchange. By utilizing the long-lived luminescence of Ln(3+), we demonstrate its application as a sensitive time-resolved fluorescence resonance energy transfer (FRET) bioprobe to detect avidin with a record-low detection limit of 3.0 nM. The oxide nanoparticles also exhibit specific recognition of cancer cells overexpressed with urokinase plasminogen activator receptor (uPAR, an important marker of tumor biology and metastasis) and thus may have great potentials in targeted bioimaging.     

Rotational dynamics of solvated carbon dioxide studied by infrared, Raman, and time-resolved infrared spectroscopies and a molecular dynamics simulation

Rotational dynamics of solvated carbon dioxide (CO(2)) has been studied. The infrared absorption band of the antisymmetric stretch mode in acetonitrile is found to show a non-Lorentzian band shape, suggesting a non-exponential decay of the vibrational and/or rotational correlation functions. A combined method of a molecular dynamics (MD) simulation and a quantum chemical calculation well reproduces the observed band shape. The analysis suggests that the band broadening is almost purely rotational, while the contribution from the vibrational dephasing is negligibly small. The non-exponential rotational correlation decay can be explained by a simple rotor model simulation, which can treat large angle rotations of a relatively small molecule. A polarized Raman study of the symmetric stretch mode in acetonitrile gives a rotational bandwidth consistent with that obtained from the infrared analysis. A sub-picosecond time-resolved infrared absorption anisotropy measurement of the antisymmetric stretch mode in ethanol also gives a decay rate that is consistent with the observed rotational bandwidths.     

Theoretical and infrared spectroscopy study of the conformational preferences for some 3-monosubstituted-2-methylpropenes

The infrared spectra of 3-X-2-methylpropenes (X = Cl, Br, I, NMe(2), NEt(2), OH, OMe, OEt, SH, SMe and SEt) have been recorded at room temperature in CCl(4) solution. The C=C stretching mode was analyzed and compared to theoretically calculated data to give insight about the conformational isomerism of these compounds. A combination band systematically appears in all spectra (except for amines); the remaining ν(C=C) band and the corresponding intensities were used to obtain the conformer populations. For second-period atoms bonded to C-3, two or more conformers are observed in CCl(4) solution, but when substitution by heavier atoms takes place, only one conformer is observed under the tested conditions, i.e., the gauche form with respect to the C=C-C-X dihedral angle. Therefore, steric hindrance between X and =CH(2) in the s-cis form is strongly dependent on the heteroatom size, while the effect of the alkyl chain bonded to the heteroatom seems to be of secondary importance.     

Investigation of hydrolysis products from uranium trioxide and uranyl salts by derivatography and infrared spectroscopy

Summary It can be established from the data obtained by derivatography and infrared spectroscopy that the hydrolysis of- and amorphous UO₃ at room temperature, and that of uranyl salts in the presence of anion exchange resins, leads to compounds of UO₃ · 2H₂O composition with identical properties. This type of compound is of complex structure containing in addition to water molecules in two kinds of bonds, hydroxyl groups as well. The relative quantities of the components with different bond strengths show that the molecular structure can be described only by a trimeric formula, or by a formula corresponding to an integral multiple of a trimeric form. One kind of water has diffuse bond strength and is probably water between individual layers, while the other is a structural water of definite bond strength which may form various hydrogen bridge bonds.

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Zusammenfassung Aus derivatographischen und IR-spektroskopischen Untersuchungen ergab sich, daß die Hydrolyse von-UO₃ und amorphem UO₃ bei Zimmertemperatur sowie die Hydrolyse von Uranylsalzen in Gegenwart von Anionenaustauschharzen zu Verbindungen der Zusammensetzung UO₃ · 2H₂O führt, die identische Eigenschaften haben. Dieser Verbindungstypus hat komplexe Struktur und enthält außer Wassermolekülen mit zwei verschiedenen Bindungsarten auch Hydroxylgruppen. Die relativen Mengen der verschieden fest gebundenen Komponenten zeigen, daß die Molekülstruktur nur durch eine trimere Formel wiedergegeben werden kann. Ein Teil der Wassermoleküle ist diffus gebunden. Dabei handelt es sich wahrscheinlich um solche zwischen einzelnen Schichten. Die anderen sind strukturell gebunden und dürften verschiedene Wasserstoffbrücken ausbilden.

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Résumé On a pu établir, à partir de données obtenues par dérivatographie et spectroscopie infrarouge, que l'hydrolyse de UO₃ et amorphe à température ambiante, ainsi que celle des sels d'uranyle en présence de résines échangeuses d'anions, conduisait à des composés de composition UO₃ · 2H₂O aux propriétés identiques. Ce type de composé est de structure complexe, contenant en plus de molécules d'eau correspondant à deux sortes de liaisons, également des groupes hydroxyles. Les quantités relatives de composants possédant des forces de liaison différentes montrent que la structure moléculaire ne peut être représentée que par une formule trimère, ou par une formule correspondant à un multiple entier d'une forme trimère. L'une des sortes d'eau possède une force de liaison diffuse et il s'agit probablement d'eau placée entre des couches individuelles, tandis que l'autre est de l'eau structurale, avec une force de liaison définie, pouvant former diverses liaisons par pont d'hydrogène.

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This paper was presented at the Symposium on Analytical Chemistry held in Graz, 29th September–1st October 1965.     

Molecular interaction of polyimide films probed by using soft-pulse dynamic compression ATR time-resolved infrared and double Fourier-transform based 2D-IR spectroscopy

An improved time-resolved step-scan Fourier transform rheo-optical system, based on the soft-pulse dynamic compression attenuated total reflection (ATR) approach, has been introduced to analyze inter-molecular interactions of poly(p-phenylene bi-phenyltetracarboximide) (BPDA–PDA) and poly(N,N-diphenyl ether bi-phenyltetracarboximide) (BPDA–ODA) films. In order to extract the full range of frequency distributions obtained from soft-pulse dynamic compression time response (relaxation) spectra, the second-Fourier transformation was applied along the relaxation time axis in addition to the interferogram axis. In the case of the BPDA–PDA, distinct periodic higher overtone bands are observed especially at C=O stretching and C=C tangential stretching vibration bands in the FFT relaxation time contour map spectra. For the BPDA–ODA, intensities of higher overtone bands are relatively weak. We have further performed 2D-IR correlation analysis at given Fourier frequencies, which includes molecular interaction information. The results suggest that the existence of molecular interaction between C=O stretching and C=C tangential stretching vibration bands.     

High pressure study of Ru3(CO)12 by X-ray diffraction, Raman, and infrared spectroscopy

The single-crystal X-ray structure of Ru(3)(CO)(12) is reported at 8 pressures ranging from 1 atm (0.0 GPa) to 8.14(5) GPa. Although intramolecular bonding parameters remain relatively constant, intramolecular and intermolecular nonbonding contact distances decrease by an average of 4% and 15%, respectively. At 8.14 GPa, O...O, C...O, and C...C intermolecular distances as short as 2.54(4), 2.64(6), and 3.07(4) A, respectively, are observed, and the unit cell compresses to 75% of the ambient pressure volume. Raman and infrared spectroscopic measurements show that carbonyl stretching frequencies shift to higher wavenumber values by as much as 80 cm(-)(1), even though Ru-C and C-O distances stay roughly constant throughout the entire pressure range studied. Compression of the sample to above 18 GPa with laser radiation results in an irreversible transformation due to either decomposition or a total collapse of D(3)(h) molecular geometry accompanied by color darkening.