Infrared spectrum of the CH3OCH2 radical in solid argon

The methoxymethyl radical, CH(3)OCH(2), is prepared via hydrogen photodissociation from dimethyl ether during codeposition of CH(3)OCH(3) in excess argon at 4 K with laser-excited metal plume radiation. The spectrum of this radical is characterized by four infrared absorptions at 1468.1, 1253.9, 1226.6, and 944.4 cm(-1), which are assigned by deuterium substitution as well as frequency and intensity calculations using density functional theory. The O-CH(2) bond length is calculated to be 0.07 ? shorter than the CH(3)-O bond due to additional π bonding interactions. In the matrix near-UV irradiation destroys the CH(3)OCH(2) radical with the formation of HCO radical and CH(4), which is different from the decomposition mechanism of CH(3)OCH(2) radical to H(2)CO and CH(3) radical proposed for the gas phase process.     

Absorption spectra and photochemistry of the toluene cation and benzyl radical in solid argon

Toluene diluted in argon subjected to continuous argon discharge radiation during condensation at 21 K revealed absorptions at 310.5 and 449.6 nm due to benzyl radical, and 317 nm due to a C₇7H₉ radical. A photosensitive 430 nm band, in agreement with photodissociation spectra of the toluene parent cation, is assigned to this species.     

Formation and characterization of the XeOO(+) cation in solid argon

This report presents the preparation and characterization of a xenon-containing cationic radical species, XeOO+. The XeOO+ cation was produced either by co-deposition of the reactive species generated by laser ablation of different transition metals with dioxygen and xenon mixtures in excess argon or by condensation of high-frequency discharged O2/Xe/Ar mixtures at 12 K and is identified by infrared absorptions. High-level quantum chemical calculations indicate that XeOO+ has a bent structure with direct xenon-oxygen dative bonding, and the doublet ground state is much more stable than the Xe + O2+ reactants.     

The absorption spectra of the phenoxyl radical in solid argon

Vacuum ultraviolet photolysis of phenol, phenol-d₆ and anisole during condensation with excess argon at 20 K has produced and trapped the phenoxyl radical as evidenced by structured absorptions at 397.2 and 628.1 nm. A broad photosensitive 416 ± 2 nm band is tentatively assigned to the phenol cation.     

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.     

Mass spectrometry for investigations of gas-phase radical cation chemistry : The two step cycloaddition of the benzene radical cation and 1,3-butadiene

Mass spectrometric techniques are now used extensively for the study of gas-phase radical cation chemistry. The generation and structural properties, the unimolecular and bimolecular chemistry of some representative radical cation systems, and the methods of study are reviewed. The structure of the ionmolecule adduct produced in the reaction of the benzene radical cation and neutral 1,3-butadiene was investigated by collisionally stabilizing the adduct and then acquiring its collision-activated decomposition spectrum. The CAD spectrum of the adduct changes dramatically as a function of the degree of collisional stabilization. This observation is interpreted in terms of two distinct structures for the adduct. The species that is stabilized at 0.7 Torr has a CAD spectrum similar to the 2-phenyl-2-butene radical cation. The second structure, stabilized at 0.1 Torr, has a CAD similar to that of 1-methylindan. The results of these experiments are interpreted in terms of a two-step cycloaddition mechanism for the formation of the 1-methylindan radical cation.     

Fluorescence spectrum of the benzyl radical in methylcyclohexane at 4.2 K

The fluorescence spectrum of the benzyl radical (BR) is characterized by participation of many totally symmetric vibrational modes with less intensity activeness. To make this point more clear, the fluorescence spectra of the benzyl radical and its deuterated compounds in methylcyclohexane (MCH) have been observed at 4.2 K and detailed vibrational analysis has been carried out. Two non-totally symmetric modes such as nu6b and nu8b play a role of Herzberg-Teller type vibronic coupling together with one totally symmetric mode nu6a. There are only a few progression bands with very weak intensity. These are nu12, nu1 and nu(phi-CH2) vibrational modes.     

High-resolution ESR spectrum of the ethynyl radical in an argon matrix at 4.2 K

The high-resolution ESR spectrum of the ethynyl radical isolated in an argon matrix at 4.2 K has been observed. The radical was produced by the in situ photolysis of acetylene. The magnetic parameters for this radical were derived by the numerical deconvolution of the spectra. It was found that, in contrast to the results reported previously by Graham [J. Chem. Phys., 60 (1974) 3817], the radicals were stabilized in three different trapping sites of the argon matrix immediately after the photolysis. The variations of the spectra in the temperature range 4.2 to 20 K were also studied.     

Electronic absorption spectrum of perylene radical cation trapped in boric acid film

A detailed spectroscopic analysis of the electronic absorption spectrum of the perylene radical cation, produced in a boric acid film by photo-oxidation is reported. To interpret the experimental spectrum, the electronic energy levels and oscillator strengths have been calculated using the Pariser—Parr molecular orbital method with limited configuration interaction. The effect of variation of solute concentration and irradiation time of the films has also been studied. It is found that the agreement between experimental and theoretical results in excellent.     

Fluorescence decay times and quantum yields for benzene in the solid and vapour phases

Fluorescence decay-tune measurements of solid benzene at very low temperature give a value of 83.8 ns which is similar, within experimental error, to the high-pressure value of benzene vapour reported in the literature. The agreement in the fluorescence quantum yield is discussed     

Infrared spectrum of Hg(OH)2 in solid neon and argon

Mercury(II) hydroxide molecules have been prepared upon mercury arc lamp irradiation of Hg, H(2), and O(2) mixtures in solid neon and argon. The strongest three infrared absorptions are identified through isotopic substitution (D(2), HD, (18)O(2), (16)O(18)O) and comparison to frequencies from DFT calculations. The isolated Hg(OH)(2) molecule is stable and has a linear O-Hg-O linkage in a C(2) structure with an 86 degrees dihedral angle. However, in aqueous solution Hg(2+) and 2OH(-) may form an Hg(OH)(2) intermediate, which eliminates water and precipitates solid HgO: The solid Hg(OH)(2) compound is not known.     

A reassignments of the EPR spectrum attributed to the radical cation of 2,2,3,3-tetramethylbutane

The EPR spectrum of γ-irradiated 2,2,3,3-tetramethylbutane has been reinvestigated. Previous evidence for the radical cation Me₃C^??CMe⁺₃ has been critically examined and it is concluded that a more satisfactory analysis can be made on the basis of the three neutral radicals ^?CH₂CMe₂CMe₃, ^?CMe₂CMe₃ and ^?CMe₃.     

Absorption spectra and photochemical rearrangement of octatetraene and decapentaene radical cations in solid argon

Parent radical cations of octatetraene and decapentaene have been prepared and trapped in solid argon using matrix photoionization methods with both cyclic and acyclic precursors. Visible absorption spectra are assigned to the all-trans cation isomer and several structures with increasing numbers of cis configurations. Irradiation into these bands with argon and krypton ion laser lines caused reversible rearrangements among several of the configurations for octatetraene and decapentaene cations. The cold matrix provides an excellent medium for studying molecular cation rearrangements where one structure can absorb light and other structures formed can be relaxed by the matrix before dissociation     

Electronic structure of the benzene dimer cation

The benzene and benzene dimer cations are studied using the equation-of-motion coupled-cluster model with single and double substitutions for ionized systems. The ten lowest electronic states of the dimer at t-shaped, sandwich, and displaced sandwich configurations are described and cataloged based on the character of the constituent fragment molecular orbitals. The character of the states, bonding patterns, and important features of the electronic spectrum are explained using qualitative dimer molecular orbital linear combination of fragment molecular orbital framework. Relaxed ground state geometries are obtained for all isomers. Calculations reveal that the lowest energy structure of the cation has a displaced sandwich structure and a binding energy of 20 kcal/mol, while the t-shaped isomer is 6 kcal/mol higher. The calculated electronic spectra agree well with experimental gas phase action spectra and femtosecond transient absorption in liquid benzene. Both sandwich and t-shaped structures feature intense charge resonance bands, whose location is very sensitive to the interfragment distance. Change in the electronic state ordering was observed between sigma and piu states, which correlate to the B and C bands of the monomer, suggesting a reassignment of the local excitation peaks in the gas phase experimental spectrum.     

Vibrational and electronic study of the methyl viologen radical cation MV+. in the solid state

A complete vibrational analysis (IR, Raman) of the methyl viologen radical cation MV^+., generated either via thermolysis from the solid MV²⁺(Cl⁻)₂ salt, or via chemical reduction from the dictation intercalated in the layered CdPS₃ compound, is reported fpr different isotopic derivatives. The results are discussed with respect to the conformation and the electronic configuration of the radical species, (MV^+.) and (MV^+.)₂.     

Multistate multimode vibronic dynamics: entanglement of electronic and vibrational degrees of freedom in the benzene radical cation

An earlier theoretical treatment of multimode and multistate vibronic coupling in the benzene radical cation [Koppel et al., J. Chem. Phys. 117, 2657 (2002)] is extended to investigate also the behavior of the nuclear degrees of freedom and to include additional electronic states. The five lowest doublet electronic states are considered which have been shown earlier to be all interconnected through a series of conical intersections of their potential-energy surfaces. In the most extensive calculations, they are all included simultaneously in the quantum dynamical calculations performed, which represent a system of unprecedented complexity treated in this way. The results are compared with various reduced-dimensionality treatments (i.e., employing reduced vibrational and electronic function spaces). The different temporal behavior of the various electronic populations is emphasized and traced to the different locations of the various seams of conical intersections: due to the coherent oscillations of the time-dependent wave packet this leads to an oscillatory behavior in some cases and to monotonous behavior in others. A seemingly irreversible behavior of the system dynamics in this strictly microscopic treatment is confirmed. The importance of this benchmark system to highlight complex, entangled multimode, and multistate vibronic dynamics is pointed out.     

A nonelectrocyclic path from the cyclobutene cation radical to the 1,3-butadiene cation radical

The conversion of the cyclobutene cation radical to the 1,3-butadiene cation radical has been studied using MINDO /3 and ab initio SCF MO methods. Not only smooth electrocyclic but also stepwise, non-electrocyclic routes were considered. Both calculational methods agree that the preferred reaction path is a novel nonelectrocyclic one proceeding through an intermediate “cyclopropylcarbinyl cation radical.” The quantitative agreement in the activation parameters calculated by the two methods is excellent. The proposed intermediate also provides an attractive explanation for the mass spectrometric fragmentation patterns of the cyclobutene and butadiene cation radicals.     

Infrared spectrum of the novel electron-deficient BH(4) radical in solid neon

Laser-ablated boron reacts with hydrogen on condensation in excess neon to give BH4 radical, BH4- anion, and B2H6 as the major products. Identifications are based on 10B and D substitution, DFT frequency calculations, and comparison to previous spectra. Infrared spectra of BH4 support the C2v structure deduced from previous ESR spectra and theoretical calculations with two normal B-H bonds and two long B-H bonds for this novel electron-deficient radical. NBO analysis suggests that the two long B-H bonds and the H- -H bond are one-electron bonds.     

Polymerization of ionized acetylene clusters into covalent bonded ions: evidence for the formation of benzene radical cation

Since the discovery of acetylene and benzene in protoplanetary nebulae under powerful ultraviolet ionizing radiation, efforts have been made to investigate the polymerization of ionized acetylene. Here we report the efficient formation of benzene ions within gas-phase ionized acetylene clusters (C2H2)n+ with n = 3-60. The results from experiments, which use mass-selected ion mobility techniques, indicate that the (C2H2)3+ ion has unusual stability similar to that of the benzene cation; its primary fragment ions are similar to those reported from the benzene cation, and it has a collision cross section of 47.4 A2 in helium at 300 K, similar to the value of 47.9 A2 reported for the benzene cation. In other words, (C2H2)3+ structurally looks like benzene, it has stability similar to that of benzene, it fragments such as benzene, therefore, it must be benzene!