MCD studies of biphenyls

The magnetic circular dichroism (MCD) spectra of biphenyl derivatives with electron donating substituents at the C₄ and/or C₄′ positions of biphenyl were measured at room temperature in the wavelength regions of 200 to 350 nm. The biphenyls studied exhibited Faraday B terms caused by a magnetic coupling of the non-degenerate electronic states. A careful inspection of the MCD spectra has enabled us to find hidden bands which were buried in the intense, so-called “conjugation band” of biphenyl, resulting in the preferable assignments of the bands.     

Magnetic circular dichroism of some cyano-substituted cyclopentadienide anions

MCD spectra of pentacyanocyclopentadienide anion, tetracyanocyclopentadienide anion and diazotetracyanocyclopentadiene were measured. They all exhibited the Faraday A term or B terms which are caused by π → π^* electonic transitions of the compounds. Transition energies and symmetries of the excited states were calculated by use of the Pariser-Parr-Pople method. The results of the calculations gave a qualitative interpretation of the observed MCD spectra.     

Magnetic circular dichroism of the 3A2g → 3T2g band of MgO: Ni2+

The absorption and magnetic circular dichroism (MCD) spectra of the ³A_2g → ³T_2g transition in Ni²⁺:MgO have been studied. MCD data confirm the magnetic dipole character of the zero-phonon lines. The phonon side bands can be explained in terms of an A_1g lattice mode.     

Vibrational spectra of the ethylenediammonium ion in crystals

The IR and Raman spectra of three isotopic varieties of the ethylenediammonium ion in the tetrachlorocadmate(II) have been measured. It is shown that the ion assumes the centrosymmetric trans conformation in this salt. A complete vibrational assignment has been proposed for the observed fundamentals. Certain assignments for related compounds in the literature are modified. The spectra of the ion in the hexachloroplatinate(IV) and hexachlorostannate(IV) have also been obtained; compared to these two compounds hydrogen bonding in the tetrachlorocadmate is appreciable. Combination bands observed in the 2100-1800 cm^?1 region of the IR and Raman spectra of compounds containing the C-NH₃⁺ grouping are discussed and assignments are suggested for those observed in ethylenediammonium salts.     

The magnetic circular dichroism spectrum of acetylene

The magnetic circular dichroism (MCD) spectrum of gas phase acetylene has been studied in the spectral region 320-140 nm. No MCD signal was detected in the region of the first transition. The observation of irregular MCD bands beginning at 185 nm confirm assignment of this latter band as the 0-0 band of the second transition. The discrete and relatively narrow bands in the region 155-140 nm exhibit pure A-term character, lending unambiguous confirmation to the assignment of ¹Π_u for the state. The observed absorption spectrum in this region is interpreted as consisting of two non-interacting systems, one involving the ¹Π_u Rydberg state and the other, a broad continuous background, cannot be assigned. It is however suggested that it may be due to the ¹Σ_u⁺ state of the π → π^* excited configuration.     

Absorption and magnetic circular dichroism spectra of matrix isolated Ta atoms

The absorption and magnetic circular dichroism (MCD) spectra of Ta atoms isolated in an argon matrix at 14 K have been measured. Over sixty-five MCD bands have been observed and used together with gas phase intensity and energy pattern data to reassign the matrix spectrum. The observed matrix shift (average: 765 cm^?1) to the blue is smaller than determined by previous workers. From this study it is suggested that the assignment of matrix-isolated atomic species can be considerably aided by the determination of their magnetic circular dichroism spectra.     

The long-wavelength MCD of some quinones and its interpretation by semi-empirical MO methods

Long-wavelength MCD spectra of several quinones are measured in solution at a magnetic field strength of 5.26 T. The B terms for the ππ^* transitions are computed with wavefunctions of the PPP type. The results enable one to deduce the polarization of many of the ππ^* bands. The signals due to nπ^* transitions are identified with the help of CNDO calculations. A very weak long-wavelength A term appearing in the spectra of some of the compounds is identified as due to the S_OT₁ (³nπ^*) absorption.     

Analysis of the D1 Δ—X1Σ+ transition in CO observed by two-photon excitation

The D¹ Δ—X¹Σ⁺ transition in carbon monoxide has been observed by two-photon excitation with a frequency-doubled pulsed dye laser. The rotational structure of thirteen υ′= 0 bands has been analyzed: the υ′= 6–12 bands in ¹²C¹⁶O, υ′= 7, 10 and 12 in ¹³C¹⁶O, and υ′= 7, 10 and 12 in ¹³C¹⁸O. Detailed assignments are presented, and from them the rotational and vibrational constants of the D¹ Δ state have been determined. Using a single mass-reduced fit, molecular constants are calculated for all three isotopomers. Analysis of the 7-0 band of the I¹Σ⁻−X¹Σ⁺ transition is also given.     

Vibrational spectra and structure of the heptahydrodiborate ion, [B2H7]− in glycol ethers

The i.r. and Raman spectra of the heptahydroborate ion, [B₂H₇]⁻, and its deuterated derivative, [B₂D₇]⁻, have been obtained in solution and assignments have been made of the observed bands. The data are interpreted as indicating a bent C₂ structure in solution. Normal coordinate calculations based on this model are presented.     

The first experimental observation of electronic transitions in C2+ and C2D+

High-resolution translational energy spectroscopy (up to 0.1 eV) has been carried out on 8 kV of C₂⁺ and C₂D⁺. The spetra obtained with C₂⁺ formed by different methods show considerable differences which are attributed to the formation of different spin states of the ion. Tentative assignments for the observed transitions have been made including one corresponding to excitation of the ⁴∑_g^? —X ⁴∑_g^? system, which may be useful as a probe of interstellar C₂⁺. Two broad transitions have been seen in the translational energy spectrum of C₂D⁺ which are in reasonable agreement with existing theoretical calculations. Tentative assignments are proposed for these transitions.     

Fluorescence spectroscopy of C60 in toluene solutions at 5 K

We have recorded the dispersed fluorescence and the fluorescence excitation spectra of C₆₀ in toluene matrices at 5 K. Upon excitation with the green Ar⁺ laser line (λ=514 nm) we obtained for the first time in this matrix well resolved visible fluorescence spectra which we have compared with those observed in other low temperature matrices. Our spectra were interpreted and assigned using theoretical assessments of vibronic activities of transitions between the three lowest excited electronic states ¹T_1g, ¹T_2g, ¹G_g and the totally symmetric ground state, and on the basis of a single 0⁰ level which has pseudo-Jahn–Teller (JT) components of the three near-degenerate excited states. The fluorescence spectra exhibit prominent JT induced h_g(1) progressions, Herzberg–Teller-induced h_u and other ungerade mode vibrations, including a very active t_1u(4) mode. Excitation wavelength independent bands are assigned to the fluorescence of C₆₀ molecules in toluene microcrystals embedded in the toluene glass whereas excitation wavelength dependent features are interpreted as originating from C₆₀ molecules isolated in the toluene glass itself. These interpretations are supported by the results of spectrally selective detected fluorescence excitation spectra.     

The electronic and magnetic circular dichroism spectra of matrix-isolated scandium atoms and the scandium dimer

The electronic and magnetic circular dichroism (MCD) spectra of scandium atoms isolated in argon, krypton and xenon matrices have been measured and the bands assigned. Some aspects of the assignment present problems and the resulting matrix shifts are rather irregular. Magnetization studies of the above systems are also reported and the data show that there are particularly strong guest—host interactions in the case of Sc/Xe. Furthermore, they suggest that there is significant guest—host interaction in the ground electronic state. Computer simulation of the magnetization curves and the MCD spectra, using a crystal field model, enables some tentative suggestions concerning the nature of the matrix sites to be made. All sites show an axial character. MCD bands of a scandium dimer have been observed. The form and magnetization properties of one band support a ⁵Σ ground state for the molecule.     

The magnetic circular dichroism of the A band in CF3I,C2H5I and t-BuI

The MCD (magnetic circular dichroism) of CF₃I, C₂H₅I and (t-BuI has been studied in the A band region (n→σ^* continuum). A complex MCD signal was observed for all these molecules. The contribution of the excited electronic states to the A band is resolved and the results are compared with data obtained using other experimental techniques.     

Magnetic circular dichroism spectra of 1,5-naphthyridine

The absorption and MCD spectra of 1,5-naphthyridine (1) are reported. The transition energies, oscillator strengths and Faraday B terms computed within the PPP SCF π MO Cl method are in reasonable agreement with experiment. The Faraday B terms of two bands in the middle wavenumber region [(30.0–45.0) × 10³ cm^?1] of 1 are larger than those in quinoline.     

Time-resolved resonance raman spectra and decay kinetics of triplet anthracene in fluid media

Reported here are the time-resolved resonance Raman spectra and decay kinetics of the lowest triplet state (³B_2u⁺) of anthracene-h₁₀ and anthracene-d₁₀ molecules in fluid media at room temperature. The triplet population (≈3 × 10^?5 M) is observed to decay at microsecond times by triplet—triplet annihilation. Vibrational assignments for the observed Raman bands are proposed.     

Magnetic circular dichroism and absorption spectra of the mononegative and dinegative ions of [16] annulene

The magnetic circular dichroism (MCD) and absorption spectra of the mononegative and dinegative ions of [16] annulene have been measured in the 16000–30000 cm^?1 region. The results are interpreted using a PPP molecular orbital calculation. It is found that the D_4h symmetry, using Slater type atomic orbitals excellent agreement between experiment and calculations is obtained. The excited ²E_g and ¹E_u states of the mono- and dinegative ions have experimental averaged angular monomenta of 1.0 h and 2.3 h respectively and we conclude to planar ring structures for the ions. Variations in the parameters for the PPP calculations, i.e. B, do not influence the MCD values to any great extent.In addition, from temperature dependent measurements between 20°C and ?150°C, the thermodynamic parameters ΔH and ΔS for the equilibrium observed between molecule and ions in solution have been determined.     

The configuration of transition metal coordination compounds containing the anion of hexahydro-1,3,5-triazine-1,3,5-triol

The configuration of Ni(IV), Fe(IV), Mn(IV) and V(IV) complexes of the type M^I₂[M^IVL₂] where M^I=Li, Na, K, Rb and Cs and the ligand L is the anion C₃H₆N₃O³⁻₃ of hexahydro-1,3,5-triazine-1,3,5-triol has been obtained by studying the infrared spectra of the complexes in the region 4000-50 cm⁻¹. Vibrational assignments for the observed bands of the complex ions have been made assuming the molecular symmetry D_3d. The assignments have been based on the observed isotopic frequency shifts due to the substitutions H/D, ¹⁴N/¹⁵N, ¹²C/¹³C, ⁵⁸Ni/⁶²Ni and ⁵⁴Fe/⁵⁷Fe and on the assignment of the bands in the infrared spectrum of hexahydro-1,3,5-triazine-1,3,5-triol, C₃H₆N₃ (OH)₃.     

Electronic and vibrational IR MCD in the Creutz-Taube complex

The Creutz-Taube complex was analysed in terms of a simple electronic coupling model and predictions of electronic transitions in the mid-IR (1800–4000 cm⁻¹) were made. Low-temperature MCD measurements in this region show broad features around 2000 and 4000 cm⁻¹ and sharp features near 3200 and 4800 cm⁻¹. Deuteration of the ammine protons indicates that the sharper features are vibrational MCD of anomalous intensity and the broader features are electronic with substantial vibronically induced intensity in the 4000 cm⁻¹ region. Measurements were made by incorporating the complex in a modified PTFE (nafion) film. Thin nafion films are transparent throughout the near- and mid-IR regions and are optically isotropic and transparent. The spectra appear to be the first C-term IR MCD spectra.     

Raman study on pentacene:C60 bulk heterojunction films

We measured 785 nm excited Raman and infrared spectra of pentacene-d₁₄. The observed spectra were assigned on the basis of the Raman and infrared spectra calculated by the density functional theory (DFT) method at the B3LYP/6⬜311 + G** level. We measured 785 nm excited Raman spectrum of a pentacne-d₁₄:C₆₀ bulk heterojunction film. The spectrum was assigned on the basis of the wavenumber shifts upon deuteration of pentacene. The assignments of the 1462 and 493 cm^↙1 A_g bands of C₆₀ were confirmed. The 511, 453, and 256 cm^↙1 bands, which were observed only in pentacene:C₆₀ bulk heterojunction films, did not show large deuteration shifts. This result indicates that the 511, 453, and 256 cm^↙1 bands are attributed to activation of the silent modes of C₆₀ due to symmetry lowering_.     

The conformation and vibrational spectra of 1,5-hexadiene-3-yne (divinylacetylene) and perchloro-1,5-hexadiene-3-yne (perchlorodivinylacetylene)

Infrared spectra of 1,5-hexadiene-S-yne (divinylacetylene) have been recorded in the vapour phase, in solution and in the amorphous and crystalline solid states at 90 K in the region 4000–4020 cm^?1. Correspondingly, IR spectra ofperchloro-1,5-hexadiene-3-yne (perchlorodivinylacetylene) as a melt, as a solute in various solvents and as a solid at 90 K have been obtained. Raman spectra of the two compounds were recorded in the liquid (molten) state including polarization measurements, and as crystalline solids at 90 K.The spectral data indicate that each compound exists as one conformer only in the various states of aggregation. In divinylacetylene the molecular symmetry appears to be anti (C_2h) while for perchlorodivinylacetylene the symmetry is either C_2v (syn) or C₂ (gauche). Vibrational assignments for the spectra of both molecules are presented and the values are compared with the results of normal coordinate analyses.