A study of the electronic spectra of 9-fluorenone

The absorption and MCD spectra of 9-fluorenone are measured. The CD spectra of the β-cyclodextrin complex with 9-fluorenone are also measured. The assignment for the first (≈26.0 × 10³ cm^?1) and fourth (≈48.0 × ³ cm^?1) absorption band has been determined from the sign of the CD spectra by reference to the observed MCD spectra.     

Induced circular dichroism spectra of 2-(2,4,6-cycloheptatrien-1-ylidene)-4-cyclopentene-1,3-dione included inβ-cyclodextrin

The assignment of the absorption spectra of 2-(2,4,6-cycloheptatrien-1-ylidene)-4-cyclopentene-1,3-dione (1) is reported by measuring the induced circular dichroism spectra of the β-cyclodextrin complex with1. It is concluded from the signs of the induced circular dichroism bands that the first absorption band (17.1×10³–34.3×10³ cm^?1) is composed of three electronic transitions having perpendicular, parallel and perpendicular polarizations with respect to the long axis (z) of1. The second absorption band (34.3×10³–42.8×10³ cm^?1) is composed of two electronic transitions having parallel polarizations with respect to the long axis of1 and the third absorption band (42.8×10³–47.1×10³ cm^?1) has the transition dipole moment perpendicular to the long axis of1. Our experimental assignments are supported by CNDO/S CI calculations.     

Interpretation of the optical dephasing time and lineshape function in the S0 → T1 exciton transitions of 1,4-dibromonaphthalene

The lineshape function for the S₀ → T₁ absorption in 1,4-dibromonaphthalene (DBN) is analyzed in terms of exchange theory. It is shown that the dominant optical dephasing mechanism for the electric dipole transition to the k = 0 state in the band results from the absorption and emission of a low energy optic phonon. This process dephases the optical absorption because of frequency differences of the phonon in the ground and excited state. In addition, it is shown how to extract the energy of the phonon responsible for dephasing, the phonon absorption rate, and the lifetime in the phonon promoted state from the data. The analysis of the data for DBN shows that very little dephasing of the optical transition occurs before ≈ 15 K but from 15 K to ≈ 40 K the singlet-triplet transitions to site I (20192 cm^?1) and site II (20245 cm^?1) are dephased by absorption and emission of an ≈ 38 cm^?1 and 45 cm^?1 phonon respectively. The phonon absorption rates by the k = 0 state in the exciton band are similar for both sites being 5 × 10⁶ s^?1 and 3 × 10⁵ s^?1 at 4 K and 7 × 10¹¹ s^?1 and 4 × 10¹¹ s^?1 at 30 K for site I and II respectively. Finally, the lifetimes in the phonon promoted state for sites I and II are 0.23 and 0.28 ps over the range 15–40 K.     

The circular dichroism spectra of the cyclodextrin complex with 1,4-benzocyclooctenedione

The assignment of the absorption spectra of 1,4-benzocyclooctenedione (1) is reported by measuring the circular dichroism spectra of the β-cyclodextrin complex with 1. It is concluded from the signs of the circular dichroism bands that the first (16.6 × 10³−27.4 × 10³ cm⁻¹) absorption band is composed of two electronic transitions having perpendicular polarizations with respect to the long axis of 1, the second (27.4 × 10³−35.8 × 10³ cm⁻¹) absorption band has the transition dipole moment parallel to the long axis of 1 and the third (35.8 × 10³−44.3 × 10³ cm⁻¹) absorption band is composed of two electronic transitions having perpendicular and parallel polarizations with respect to the long axis of 1.     

A spectrokinetic study of CH2I and CH2IO2 radicals

The UV absorption spectrum and kinetics of CH₂I and CH₂IO₂ radicals have been studied in the gasphase at 295 K using a pulse radiolysis UV absorption spectroscopic technique. UV absorption spectra of CH₂I and CH₂IO₂ radicals were quantified in the range 220–400 nm. The spectrum of CH₂I has absorption maxima at 280 nm and 337.5 nm. The absorption cross-section for the CH₂I radicals at 337.5 nm was (4.1 ± 0.9) × 10^?18 cm² molecule^?1. The UV spectrum of CH₂IO₂ radicals is broad. The absorption cross-section at 370 nm was (2.1 ± 0.5) × 10^?18 cm² molecule^?1. The rate constant for the self reaction of CH₂I radicals, k = 4 × 10^?11 cm³ molecule^?1 s^?1 at 1000 mbar total pressure of SF₆, was derived by kinetic modelling of experimental absorbance transients. The observed self-reaction rate constant for CH₂IO₂ radicals was estimated also by modelling to k = 9 × 10^?11 cm³ molecule^?1 s^?1. As part of this work a rate constant of (2.0 ± 0.3) × 10^?10 cm³ molecule^?1 s^?1 was measured for the reaction of F atoms with CH₃I. The branching ratios of this reaction for abstraction of an I atom and a H atom were determined to (64 ± 6)% and (36 ± 6)%, respectively. © 1994 John Wiley & Sons, Inc.     

Atmospheric chemistry of cyclohexanone: UV spectrum and kinetics of reaction with chlorine atoms

Absolute and relative rate techniques were used to study the reactivity of Cl atoms with cyclohexanone in 6 Torr of argon or 800–950 Torr of N₂ at 295 ± 2 K. The absolute rate experiments gave k(Cl + cyclohexanone) = (1.88 ± 0.38) × 10^?10, whereas the relative rate experiments gave k(Cl + cyclohexanone) = (1.66 ± 0.26) × 10^?10 cm³ molecule^?1 s^?1. Cyclohexanone has a broad UV absorption band with a maximum cross section of (4.0 ± 0.3) × 10^?20 cm² molecule^?1 near 285 nm. The results are discussed with respect to the literature data. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 223–229, 2008     

UV absorption spectrum of CF3CFClO2 and kinetics of the self reaction of CF3CFCl and CF3CFClO2 and the reactions of CF3CFClO2 with NO and NO2

The ultraviolet absorption spectrum of CF₃CFClO₂ and the kinetics of the self reactions of CF₃CFCl and CF₃CFClO₂ radicals and the reactions of CF₃CFClO₂ with NO and NO₂ have been studied in the gas phase at 295 K by pulse radiolysis/transient UV absorption spectroscopy. The UV absorption cross section of CF₃CFCl radicals was measured to be (1.78 ± 0.22) × 10^?18 cm² molecule^?1 at 220 nm. The UV spectrum of CF₃CFClO₂ radicals was quantified from 220 nm to 290 nm. The absorption cross section at 250 nm was determined to be (1.67 ± 0.21) × 10^?18 cm² molecule^?1. The rate constants for the self reactions of CF₃CFCl and CF₃CFClO₂ radicals were (2.6 ± 0.4) × 10^?12 cm³ molecule^?1 s^?1 and (2.6 ± 0.5) × 10^?12 cm³ molecule^?1 s^?1, respectively. The reactivity of CF₃CFClO₂ radicals towards NO and NO₂ was determined to (1.5 ± 0.6) × 10^?11 cm³ molecule^?1 s^?1 and (5.9 ± 0.5) × 10^?12 cm³ molecule^?1 s^?1, respectively. Finally, the rate constant for the reaction of F atoms with CF₃CFClH was determined to (8 ± 2) × 10^?13 cm³ molecule^?1 s^?1. Results are discussed in the context of the atmospheric chemistry of HCFC-124, CF₃CFClH. © 1994 John Wiley & Sons, Inc.     

The acetyl radical studied by flash photolysis and kinetic spectroscopy

The acetyl radical absorption spectrum is a broad band with maximum decadic extinction coefficient of (1.0 ± 0.1) × 10⁴ ? mole^?1 cm^?1 at 215 nm and an oscillator strength of 0.23 ± 0.03. Absolute rate constants were estimated as 4.5 × 10¹⁰ ? mole^?1 s^?1 for the mutual interaction of acetyl radicals, and as 7.5 × 10¹⁰ ? mole^?1 s^?1 for the cross interaction of acetyl and methyl radicals.     

Absorption and emission spectra of Ca2 in solid krypton

The calcium van der Waals molecule, Ca₂, has been formed by codepositing calcium and krypton atoms on a substrate at 12 K. Absorption spectra revealed a structured band at 666 nm with 117 ± 2 cm^? spacings. Calcium-44 isotopic spectra confirmed the assignment and located the band origin at 14 432 ± 4 cm^?1. Emission spectra, pumping the 11 ← 0 absorption, exhibited a very strong 14 000 cm^?1 band with 78 ± 2 cm^?1 spacings to the band origin and unrelaxed emission with 78 ± 2 and 117 ± 2 cm^?1 spacings above the band origin from v′ levels up to 6. The transition ¹∑⁺_u(¹S + ¹P) ← ¹∑⁺_g (¹S + ¹S) and the bonding in ground and excited Ca₂ states fit a simple molecular orbital model.     

The infrared spectra of amorphous solid water and ice Ic between 10 and 140 K

Absorption spectra from 4000 to 1200 cm^?1 of amorphous solid water and polycrystalline ice I_c have been measured between 10 K and 140 K. Warm up and recooling of an H₂O sample prepared at 10 K gives rise to both irreversible and reversible changes in the peak frequency, band width, and peak height as well as the integrated intensity of the OH stretching band. These spectral effects are related to structural differences. The structure of amorphous solid water also depends on deposition conditions. The optical constants of amorphous so water are determined at 10 K and 80 K from a Kramers-Kronig analysis of the transmission spectra taking into account reflection and interference losses. The astrophysical implication of the temperature dependence of peak frequency and band width of the 3250 cm^?1 band in amorphous solid water is discussed briefly.     

Rate constants for the reactions of O3 and OH radicals with a series of alkynes

Rate constants for the reactions of O₃ and OH radicals with acetylene, propyne, and 1-butyne have been determined at room temperature. The rate constants obtained at 294 ± 2 K for the reactions of O₃ with acetylene, propyne, and 1-butyne were (7.8 ± 1.2) × 10^?21 cm³/molecule · s, (1.43 ± 0.15) × 10^?20 cm³/molecule · s, and (1.97 ± 0.26) × 10^?20 cm³/molecule · s, respectively. The rate constants at 298 ± 2 K and atmospheric pressure for the reactions with the OH radical, relative to a rate constant for the reaction of OH radicals with cyclohexane of 7.57 × 10^?12 cm³/molecule · s, were determined to be (8.8 ± 1.4) × 10^?13 cm³/molecule · s, (6.21 ± 0.31) × 10^?12 cm³/molecule · s, and (8.25 ± 0.23) × 10^?12 cm³/molecule · s for acetylene, propyne, and 1-butyne, respectively. These data are discussed and compared with the available literature rate constants.     

Absorption and emission spectra of the lowest triplet state in hexachloroacetone

T₁ ← S₀ absorption and T₁ → S₀ phosphorescence spectra of neat cystalline hexachloroacetone have been analyzed at 4.2°K. From the lifetime and energy the upper state is assigned as ³nπ^*. The spectra are sharp compared to other aliphatic ketones, with the 0-0 band at 26 248 ± 2 cm ^?1. The phosphorescence shows two strong progressions; one involving the CO stretching mode at 1784 cm^?1 (x), the other a long progression of at least 8 bands involving a mode at 143 cm^t-1 (a). The 143 cm^?1 progression forming mode can best be asigned to the CO out-of-plane wagging vibration. The absorption shows the same two strong progressions, reduced in frequency to 1270 cm^t-1 and 123 cm^?1, respectively, but with the progression in mode a broadened with increasing n. The broadening is interpreted as arising from inversion doublets; the close harmonicity up to n = 5 allowing the potential barrier to inversion to be estimated as > 700 cm^?1. A feature of the spectra is the absence of low frequency torsional modes suggesting lack of pseudo Jahn-Teller distortion of the triplet state potential surface. For comparison, the phosphorescence of crystalline hexafluoroacetone was also studied at 4.2°K. The spectrum exhibits broad bandedness with a 00 band tentatively assigned at 26 870 ± 20 cm^?1.     

Computer deconvolution applied to the parallel band, ν9 + ν10, of hexadeuteroethane

Computer deconvolution of spectra is discussed, and a close comparison made of deconvoluted spectra with those measured at higher resolution. It is shown that spectra at a resolution of ～0.012 cm^?1 can be obtained by the use of a relatively small grating spectrometer.The parallel band, ν₉ + ν₁₀, of C₂D₆ is examined at a resolution of 0.012 cm^?1 but no K-structure is observed, indicating that (A′?B′)?(A″?B″) is less than 1 × 10^?5 cm^?1. Rotational constants are given for the main band and two hot bands.     

The pressure and temperature dependence of the rate constant for methyl radical recombination over the temperature range 296–577 K

The rate constant for methyl radical recombination has been measured over the temperature range 296–577 K and at pressures between 5 and 500 Torr using laser flash photolysis, coupled with absorption spectroscopy at 216.36 nm. Analysis of the fall-off curves gives k_∞ = (2.78 ± 0.18) × 10^?11 exp(154 ± 22 K/T) cm³ molecule^?1 s^?1 and k₀ = (6.0 ± 3.3) × 10^?29 exp(1680 ± 300 K/T) cm⁶ molecule^?2 s^?1. The quoted errors (two standard deviations) do not include the present uncertainty in the absorption cross section, which is a major source of error (± 30%).     

The Structure and Properties of Phenol-2,4-disulfonic Acid Dihydrate

The crystal and molecular structure of phenol-2,4-disulfonic acid dihydrate was determined by X-ray structure analysis. All hydrogen positions in the crystal structure were found using difference Fourier syntheses. Oxonium cations and acid anions were linked in the crystal structure by short H-bonds, and the phenol OH group participated in two weak H-bonds with sulfo group oxygens simultaneously. The IR frequency corresponding to ν_{s, as} (H₃O⁺) vibrations decreased to 2700 cm^?1 under the influence of short H-bonds between oxonium cations and anions. The contour of the corresponding absorption band became anomalously broad. A discrete maximum was observed at 3412 cm^?1 on the high-frequency wing of this band; this maximum was assigned to OH stretching vibrations of the phenol group. The protonic conductivity of the compound measured by impedance spectroscopy was 2.5 × 10^?6 Ω^?1 cm^?1 at 298 K in a vacuum, E _a = 0.37 ± 0.01 eV. An increase in the humidity of the environment to 15% at room temperature increased conductivity from 10^?6 to 10^?5 Ω^?1 cm^?1, E _a = 0.27 ± 0.02 eV.     

A consistent model for the thermal decomposition of NCN3 and the singlet– triplet relaxation of NCN

The thermal decomposition of cyanogen azide (NCN₃) and the subsequent collision‐induced intersystem crossing (CIISC) process of cyanonitrene (NCN) have been investigated by monitoring excited electronic state ¹NCN and ground state ³NCN radicals. NCN was generated by the pyrolysis of NCN₃ behind shock waves and by the photolysis of NCN₃ at room temperature. Falloff rate constants of the thermal unimolecular decomposition of NCN₃ in argon have been extracted from ¹NCN concentration–time profiles in the temperature range 617 K <T< 927 K and at two different total densities: k(ρ ≈ 3 × 10^?6 mol/cm³)/s^?1=4.9 × 10⁹ × exp (?71±14 kJ mol^?1/RT) (± 30%); k(ρ ≈ 6 × 10^?6 mol/cm³)/s^?1=7.5 × 10⁹ × exp (‐71±14 kJ mol^?1/RT) (± 30%). In addition, high‐temperature ¹NCN absorption cross sections have been determined in the temperature range 618 K <T< 1231 K and can be expressed by σ /(cm²/mol)= 1.0 × 10⁸ ?6.3 × 10⁴ K^?1 × T (± 50%). Rate constants for the CIISC process have been measured by monitoring ³NCN in the temperature range 701 K <T< 1256 K resulting in k_CIISC (ρ ≈ 1.8 ×10^?6 mol/cm³)/ s^?1=2.6 × 10⁶× exp (‐36±10 kJ mol^?1/RT) (± 20%), k_CIISC (ρ ≈ 3.5×10^?6 mol/cm³)/ s^?1 = 2.0 × 10⁶ × exp (?31±10 kJ mol^?1/RT) (± 20%), k_CIISC (ρ ≈ 7.0×10^?6 mol/cm³)/ s^?1=1.4 × 10⁶ × exp (?25±10 kJ mol^?1/RT) (± 20%). These values are in good agreement with CIISC rate constants extracted from corresponding ¹NCN measurements. The observed nonlinear pressure dependences reveal a pressure saturation effect of the CIISC process. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 30–40, 2013     

Far infrared spectrum of silane

The absorption spectrum of SiH₄ from 32 to 400 cm^?1 has revealed two sepasrate bonds,one linear in density and one quadratic.From the linear band,the electric dipole moment produced in the ground vibronic state by centrifugal distortion effects has been estimated to be 9.3 × 10^?6 D in magnitude. From the quadratic band, the molecular octopole moment has been determined to be 3.0 × 10^?34 esu cm³ in magnitude. The simplicity of the techniques used is stressed.     

Pyrolytic production of Se (3P) from carbon diselenide. II. Rate of CSe2 decay

Pyrolytic decay of carbon diselenide was monitored by ultraviolet absorption spectroscopy in reflected shock waves in the temperature range of 1600–2600°K. The temperature dependence of the absorption coefficient of CSe₂ at 2308 Å was determined and was used to provide kinetic information along with a deconvolution procedure which accounted for and removed systematic distortions of the fast time-resolved absorbance profile. For temperatures of 1600–2600°K and argon densities of 1.5–7.0 × 10^?5 mol/cm³ dilute (1.0–9.0 × 10^?9 mol/cm³) CSe₂ pyrolyzed with measured first-order decay rates in the range of log₁₀ k₁ (sec^?1) = 3.0?5.7; at midrange (2100°K and 4.3 × 10^?5 mol/cm³ in Ar) k₁ ≈ 3 × 10⁴ sec^?1. The decay probably occurs via a unimolecular low-pressure process, first order in both CSe₂ and Ar, for which k₂ ± 10⁹ cm³/mol·sec at 2100°K. The deconvoluted data yield Arrhenius activation energies of 53.2 kcal/mol under second-order treatment, but the activation energy is less reliable than the general magnitude of the rate constant. A comparison of CSe₂ with other molecules which are isoelectronic in their valence shells (CO₂, CS₂, OCS, and N₂O) is made.     

The UV absorption spectrum of the CCl3 radical and the kinetics of its mutual combination reaction from 253 to 623 K

The UV absorption spectrum and the kinetics of the self combination reaction of the CCl₃ radical were studied by flash photolysis in the temperature range 253–623 K. Experiments were performed at the atmospheric pressure, except for a few runs at the highest temperatures, which were performed between 30 and 760 torr. CCl₃ radicals were generated by flash photolysis of molecular chlorine in the presence of chloroform. The UV spectrum exhibits a strong unstructured band between 195 and 260 nm with a maximum at 211 ± 2 nm. The absorption cross section, measured relative to σ(HO₂), is σ(CCl₃) = (1.45 ± 0.35) × 10^?17 cm² molecule^?1 at the maximum. This value takes into account the uncertainty in σ(HO₂) which was taken equal to (4.9 ± 0.7) × 10^?18 cm² molecule^?1. The absolute rate constant for the CCl₃ mutual combination was determined by computer simulation of the transient decays. The rate constant, which exhibits a slight negative temperature coefficient, can be expressed as: The study of the pressure dependence showed that only a slight fall-off behavior could be observed at the highest temperature (623 K). This result was corroborated by RRKM calculations which showed that the rate constant is at the high pressure limit under most experimental conditions below 600 K.     

The frequency,fluence, and pressure dependence of the absorption of pulsed CO2-laser radiation by SF6 at 140 K

We report measurements of absorption of pulsed CO₂ laser radiation by SF₆ at 140 K. These measurements cover a broad range of fluence (10^?6 to 0.8 J/cm²), SF₆ gas density (2 × 10¹⁵ to 6 × 10¹⁶ cm^?3), and frequency (six CO₂-laser frequencies within the SF₆ v₃ band). We employ two methods of data reduction including one that gives a simple phenomenological function of the three principal independent variables. We conclude that at low fluence a small fraction of the SF₆ molecules absorb the laser radiation and that collisions and higher fluence both increase that fraction. At higher fluence absorption by vibrationally excited molecules becomes increasingly important.