The resonance Raman spectrum of the aniline radical cation

The time-resolved resonance Raman spectrum of the aniline radical cation has been observed using pulse radiolysis methods. This radical exhibits a large inverse secondary isotope effect on deuteration of the NH₂ group on the CN stretching frequency. Various spectral features indicate that this radical is structurally similar to the phenoxyl radical.     

Coordination of extraframework Li+ cation in the MCM-22 and MCM-36 zeolite: FTIR study of CO adsorbed

Nature and population of Li⁺ cationic sites in MCM-22 zeolite and its pillared form (MCM-36) were investigated by means of adsorption of CO as a probe molecule. CO stretching frequency and adsorption heat were measured by FTIR spectroscopy and adsorption microcalorimetry. Intrazeolitic carbonyl complexes on Li⁺ cations in MCM-22 and MCM-36 are characterized by two main vibrational bands at 2,195 and 2,188 cm^?1. Band at higher wavenumbers is ascribed to carbonyls on Li⁺ ions coordinated only to two oxygen atoms at the intersection of 10-ring channels and interacting with CO molecule by energy around 45 kJ mol^?1. Band at 2,188 cm^?1 was assigned to the carbonyls on Li⁺ cations located on top of 5 or 6-rings on the channel walls and coordinated to three or four oxygen atoms, interacting with CO molecule by energy 33–36 kJ mol^?1. Effect of pillaring and layered form of zeolite on nature and population of Li⁺ cationic sites is also discussed, as well as the formation of dicarbonyl complexes.     

The alkali metal cation effect on the surface-enhanced Raman spectra of phosphate anions adsorbed at silver electrodes

The interaction of adsorbed phosphate anions with alkali metal cations at the Ag|aqueous solution interface has been investigated by surface-enhanced Raman spectroscopy (SERS). Formation of ion pairs at the interface was evident from the cation-induced perturbations in the SER spectra of anions. The frequency of the external vibration, silver–oxygen (Ag---O′), was not sensitive to the nature of cation, while the relative intensity of this mode was cation-dependent and was explored as a sensitive probe for the monitoring of coadsorption of ions at the interface. From the internal phosphate vibrations, both asymmetric modes, δ_as(PO) and ν_as(PO), were found to be the most sensitive to the nature of the cation. At a relatively positive potential (0.00 V vs. Ag | AgCl) the spectral parameters for the Cs⁺ and K⁺ cations were very similar indicating the same bonding type with anions. A more inhomogeneous chemical environment for the phosphate oxygen atoms was detected in the case of Na⁺ and Li⁺ cations. An increase in ν_as(PO) frequency by ca. 10 cm⁻¹ was the characteristic spectral signature for the interaction of phosphates with Li⁺. The formation of water-shared ion pairs at the interface was suggested based on the absence of splitting in the ν_as(PO) mode and the previously observed frequency sensitivity of this band to solvent H₂O substitution by D₂O. At negative potential (−0.80 V), a stabilization effect of Cs⁺ on the phosphate adlayer was detected based on the twofold increase in intensity of the ν(Ag---O′) mode compared with Li⁺. Splitting of the ν_as(PO) mode suggested the contact interaction of anions with specifically adsorbed Cs⁺ cations.     

Fluorescence studies of pyrenealdehyde adsorbed within zeolite supercages

The absorption and fluorescence of pyrenealdehyde have been utilized to probe the nature of sites in solid zeolites that adsorb aromatic molecules. In addition to substantial spectral shifts, excimer formation is found for pyrenealdehyde adsorbed on type Na⁺Y zeolites. A similar enhancement of excimer formation is noted for γ-cyclodextrins in aqueous solutions of pyrenealdehyde.     

Structure and catalytic function of Re-oxo species grafted onto H-MFI zeolite by sublimation of Re2O7

Isolated Re-oxo species within spatially constrained MFI zeolite channels were synthesized via exchange with Re2O7 vapor and shown to exist as isolated Re-oxo monomers. Turnover rates and Re-oxo structures did not depend on Re content. These materials were thermally stable and catalyzed alcohol oxidation reactions at unprecedented rates and near ambient temperatures.     

Time-resolved electronic Raman spectrum of terbium aluminum garnet excited with visible and UV laser sources

Excitation profiles for the intensities of electronic Raman transitions between crystal field components of the ⁷F₆ and ⁷F₅ manifolds of terbium aluminum garnet are recorded for excitation in the spectral region where absorption bands due to levels of the ⁵D₄ manifold occur. The intensities of the electronic transitions are not enhanced which is thought to be caused by the small values of electric dipole matrix elements of the resonating electronic states in comparison to the values of such elements to other intermediate states which occur in the expression for the scattering tensor. Fluorescence from the ⁵D₄ levels is induced and resonance fluorescence are time resolved with respect to the Raman transitions. We report electronic Raman transitions excited with the 308.0 nm line of an XeCl excimer laser. As opposed to excitation with visible laser sources, transitions are recorded which terminate on all the crystal field levels of the ⁷F_5…0 levels. In addition, fluorescence from ⁵D₃ to the ground state of terbium aluminum garnet is also observed.     

Raman spectrum of difluorodiazirine

The Raman spectrum of difluorodiazirine has been re-examined. Four well-defined bands have been found in the low frequency region, which lead to a definitive assignment for all nine vibrational fundamentals of this molecule. The fundamental frequences are (in cm⁻¹): (a₁) 1563, 1282, 805, 502; (a₂) 451; (b₁) 1248, 481; (b₂) 1091, 544.     

The electronic states of naphthalene molecules adsorbed on a zeolite

Physical principles are considered for this method of examining interactions. Changes in absorption and fluorescence spectra are examined in relation to Van der Waals, electrostatic, and exchange interactions. Major spectral criteria are presented for the types of interaction and are illustrated by reference to naphthalene adsorbed on zeolites. Spectra at 77 K show that the adsorbed molecules are in two different states: in one they are bound by Van der Waals forces, while in the other a charge-transfer complex is formed. Examination at intervals after preparation shows that the adsorbed naphthalene is gradually oxidized.     

Vibrational spectrum of the tropylium cation

Russian Chemical Bulletin -     

Spectroscopic evidence for a persistent benzenium cation in zeolite H-beta

Experimental evidence of protonation of an aromatic ring by a zeolite is hereby presented for the first time. The changes in vibrational properties and electronic transitions of the highest polymethylbenzene homologue, that is, hexamethylbenzene, were investigated after introducing the compound directly into a H-beta zeolite. Protonation of the aromatic ring, and thus the loss of symmetry, activated a vibrational ring mode at 1600 cm(-)(1). Furthermore, an electronic transition around 26 000 cm(-)(1), which was totally absent for the neutral species, was an obvious consequence of protonation. A parallel study of hexamethylbenzene adsorbed on a beta zeolite virtually free from protons did not show those distinctive spectral features. On the basis of the gas-phase proton affinity of hexamethylbenzene, a complete proton transfer from the zeolite framework to the molecule is, according to conventional considerations, not expected. The hexamethylbenzenium ion is stable in the zeolite cavities at least up to 200 degrees C. The remarkable persistence of this carbenium ion may be attributed to spatial constraints imposed by the tight fit of the cation inside the zeolite channels. Hexamethylbenzene is a relevant reaction intermediate in the methanol-to-hydrocarbons reaction and also plays a central role as a coke precursor in zeolite-catalyzed reactions that involve polymethylbenzenes.     

Effect of metal cation on photoisomerization of azobenzenes in zeolite nanocavities

In the photostationary state, the cis/trans isomer ratio of azobenzene and 3,3′-dimethylazobenzene adsorbed in zeolite NaY increases significantly to ca. 90:10, in contrast to the reaction in cyclohexane. However, for azobenzene-4,4′-dicarboxylic acid diethyl ester the formation of the cis isomer is remarkably suppressed to ca. 30%. On the basis of ab initio MO calculations, it is suggested that electrostatic interaction between these azobenzenes and the metal ions in zeolite nanocavities regulates the cis-trans photoisomerization process. In addition, it is found that the photoisomerization behavior of azobenzenes adsorbed on silica gel is similar to that in NaY.     

Raman spectrum of propylene carbonate

The Raman spectrum of propylene carbonate (4-methyl-1,3-dioxolan-2-one) has been recorded and analyzed. Vibrational assignments have been made for many of the observed frequencies on the basis of comparison with accepted assignments for certain vibrational modes in other compounds with close structural similarities.The spectra of propylene carbonate (PC)-water mixtures have been studied over the entire concentration range at 80° and there seems to be little or no interaction except for partial disruption of hydrogen bonding in water by PC. Raman spectra of solutions of LiClO₄ in PC and in PCH₂O mixtures indicate possible salvation of the Li⁺ ion.     

The Raman spectrum of propynal

The Raman spectrum of propynal as a vapour and dissolved in various solvents were recorded. These data and the observed polarization measurements were in accordance with the fundamental frequencies assigned to the ground state of this molecule. The vibrational modes of propynal were compared with those previously reported for the halopropynals.