Two-Photon Absorption and Excited-State Refractions in Anthraquinone Dyes

We examine the nonlinear optical properties of solutions of 9,10-anthraquinone, 1,4-dihydroxy-anthraquinone, 5,8-dichloro-1,4-dihydroxy-anthraquinone and 1,4-bisethylamino-anthraquinone by means of the intensity-dependent transmission and the Z-scan method with 532 nm 8 ns pulses. The results demonstrated that the 9,10-anthraquinone displayed a two-photon absorption (TPA) character. The molecular TPA cross section of this compound is estimated as σ₂ = 7.22 × 10^?19 cm⁴/GW or σ₂ = 26.96 × 10^?48 cm⁴/photon/s, respectively, and an essential state of ‘m¹Ag’, which should be located near the 2ω virtual transition state, is predicted. On the other hand, the effective excited-state nonlinear refractive coefficients n₂^eff of these anthraquinones are found to be ～10^?10 esu, which are comparable with those highly conjugated planar molecules of tetrabenzporphyrins and phthalocyanines.     

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.     

Kinetics of the association of H+3 with H2 at low temperatures

The rate constant for the formation of H⁺₅ (D⁺₅) at (86 ± 3) °K by the three-body process has been determined (k₃(H) = (2.16 ± 0.10) × 10^?28 × 10^?28 cm⁶/molecule² sec and k₃(D) = (1.47 ± 0.20) × 10^?28 cm⁶/molecule² sec) in a high pressure mass spectrometer. Comparison of this result with published rate data at 300 °K indicates the reaction has an apparent activation energy of ?1.5 kcal/mole.     

Kinetics of the reaction HO2 + NO2(+M) = HO2NO2 using molecular modulation spectrometry

Rate constants for the reaction HO₂ + NO₂(+ M) = HO₂NO₂(+ M) have been obtained from direct observations of the HO₂ radical using the technique of molecular modulation ultraviolet spectrometry. HO₂ was generated by periodic photolysis of Cl₂ in the presence of excess H₂ and O₂, and k₁ was determined from the measured concentrations and lifetime of HO₂ with NO₂ present. k₁ increased with pressure in the range of 40–600 Torr, and a simple energy transfer model gave the following limiting second- and third-order rate constants at 283 K: k₁^∞ = 1.5 ± 0.5 × 10^?12 cm³/molec·sec and k₁^III = 2.5 ± 0.5 × 10^?31 cm⁶/molec·sec. The ultraviolet absorption spectrum of peroxynitric acid was also recorded in the range of 195–265 nm; it showed a broad feature with a maximum at 200 nm, σ_max = 4.4 × 10^?18 cm².     

FTIR studies of the kinetics and mechanism for the reaction of Cl atom with formylchloride

The rate constant for the reaction Cl + CHClO → HCl + CClO was determined from relative decay rates of CHClO and CH₃Cl inthe photolysis of mixtures containing Cl₂ (～1 torr), CH₃Cl (～1 torr), and O₂ (～0.1 torr) in 700 torr N₂. In such mixtures CHClO was generated in situ as a principal product prior to complete consumption of O₂. The value of k(Cl + CHClO)/k(Cl + CH₃Cl) = 1.6 ± 0.2(3σ) combined with the literature value of k(Cl + CH₃Cl) = 4.9 × 10^?13 cm³/molecule sec gives k(Cl + CHClO) = 7.8 × 10^?13 cm³/molecule sec at 298 ± 2 K, in excellent agreement with a previous value of (7.9 ± 1.5) × 10^?13 cm³/molecule sec determined by Sanhueza and Heicklen [J. Phys. Chem., 79 , 7 (1975)]. Thus this reaction is approximately 100 times slower than the corresponding reactions of aldehydes and alkanes with comparable C? H bond energies (≤95 kcal/mol).     

A laser flash photolysis/IR diode laser absorption study of the reaction of chlorine atoms with selected alkanes

A high‐resolution IR diode laser in conjunction with a Herriot multiple reflection flow‐cell has been used to directly determine the rate coefficients for simple alkanes with Cl atoms at room temperature (298 K). The following results were obtained: k(Cl + n‐butane) = (1.91 ± 0.10) × 10^?10 cm³ molecule^?1 s^?1, k(Cl + n‐pentane) = (2.46 ± 0.12) × 10^?10 cm³ molecule^?1 s^?1, k(Cl + iso‐pentane) = (1.94 ± 0.10) × 10^?10 cm³ molecule^?1 s^?1, k(Cl + neopentane) = (1.01 ± 0.05) × 10^?10 cm³ molecule^?1 s^?1, k(Cl + n‐hexane) = (3.44 ± 0.17) × 10^?10 cm³ molecule^?1 s^?1 where the error limits are ±1σ. These values have been used in conjunction with our own previous measurements on Cl + ethane and literature values on Cl + propane and Cl + iso‐butane to generate a structure activity relationship (SAR) for Cl atom abstraction reactions based on direct measurements. The resulting best fit parameters are k_p = (2.61 ± 0.12) × 10^?11 cm³ molecule^?1 s^?1, k_s = (8.40 ± 0.60) × 10^?11 cm³ molecule^?1 s^?1, k_t = (5.90 ± 0.30) × 10^?11 cm³ molecule^?1 s^?1, with f( ? CH₂^? ) = f (? CH₂^? ) = f (?C?) = f = 0.85 ± 0.06. Tests were carried out to investigate the potential interference from production of excited state HCl(v = 1) in the Cl + alkane reactions. There is some evidence for HCl(v = 1) production in the reaction of Cl with shape n‐hexane. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 86–94, 2002     

A two-photon absorption cross section measurement in nitric oxide

We report here the measurement of a two-photon absorption cross section for the R₂₂ + S₁₂ (J″ = 9.5) [A ²Σ⁺ (ν′ = 0) - X ²Π (ν′ = 0)] transition in the gamma band system of nitric oxide by measuring the third-order susceptibility using a four-wave mixing technique. A value of σ⁽²⁾ = (1.0 ± 0.6) X 10^?38 πg(2ω₁ ? ω_f) cm⁴ s was obtained.     

Nonlinear optical properties of systems based on (tetra-15-crown-5-phthalocyaninato)indium(III)

The nonlinear optical properties of solutions of (2,3,9,10,16,17,23,24-tetra-15-crown-5-phthalocyaninato)indium(III) [(15C5)₄Pc]In(OH) in tetrachloroethane (TCE) have been studied by the z-scan method. It has been found that a nonlinear optical response is due to supramolecular associates formed in a tetrachloroethane solution by heating to 90°C/slow cooling to room temperature cycling. The formation of the supramolecular associates has been studied by atomic force microscopy (AFM) and electronic absorption spectroscopy (EAS). It has been shown that a single thermal treatment of [(15C5)₄Pc]In(OH) solutions in TCE results in the predominant formation of dimers, as evidenced by both a short-wavelength shift of the Q-absorption band of the monomeric complex (λ_max = 692 nm) to the band of λ_max = 653 nm and height doubling of molecular entities as measured by AFM. The dimers are responsible for the two-photon absorption measured in the femtosecond range, which has a relatively high cross section of σ₂ = 1.38 × 10^?46 cm⁴ s/(molecule, photon) or 1.38 × 10⁴ GM. According to the AFM data, three cycles of heat treatment of the solution leads to the formation of supramolecular assemblies of about 200 nm length. The optical spectrum exhibits long-wavelength absorption at λ_max = 841 nm and the long-wavelength edge near 1300 nm. In the case of nanosecond 1064-nm laser irradiation, the linear absorption S ₀ → S ₁ is primary, having the cross section of σ₀ = α₀/N = 2.3 × 10^?20 cm². The known high quantum yield (close to unity) of triplet states of indium phthalocyanines suggests that the main nonlinear optical effect is determined by intersystem crossing S ₁ → T ₁ and triplet-triplet absorption T ₁ → T ₂. The absorption cross section is σ _T-T = 1.14 × 10^?19 cm².     

The ultraviolet absorption by alkylperoxy radicals and their mutual reactions

Methylperoxy radicals, CH₃O₂ · have been detected by UV light absorption in the photolysis of azomethane, oxygen and nitrogen mixtures using the technique of molecular modulation spectrometry. The radical concentration is shown to be governed by second-order kinetics. The results give the extinction coefficient, o (exponential), at the peak (λ = 240 nm) = 4.4 × 10^?18 molecule^?1 cm² and a value for the rate constant of mutual recombination, k, which lies between 2.2 × 10^?13 and 4.4 × 10^?13 molecule^?1 cm³ sec^?1. Similar results have been obtained when the azomethane was replaced by azoethane, suggesting the formation of C₂H₅O₂.     

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 oxidation of methyl radicals at room temperature

Using the technique of molecular modulation spectrometry, we have measured directly the rate constants of several reactions involved in the oxidation of methyl radicals at room temperature: k₁ is in the fall-off pressure regime at our experimental pressures (20–760 torr) where the order lies between second and third and we obtain an estimate for the second-orderlimit of (1.2 ± 0.6) × 10^?12 cm³/molec · sec, together with third-order rate constants of (3.1 ± 0.8) × 10^?31 cm⁶/molec² · sec with N₂ as third body and (1.5 ± 0.8) × 10^?30 with neopentane; we cannot differentiate between k_2a and k_2c and we conclude k_2a + (k_2c) = (3.05 ± 0.8) × 10^?13 cm³/molec · sec and k_2b = (1.6 ± 0.4) × 10^?13 cm³/molec · sec; k₃ = (6.0 ± 1.0) × 10^?11 cm³/molec · sec.     

UV absorption spectra of HO2, CH3O2, C2H5O2, and CH3C(O)CH2O2 radicals and mechanism of the reactions of F and Cl atoms with CH3C(O)CH3

Pulse radiolysis techniques were used to measure the gas phase UV absorption spectra of the title peroxy radicals over the range 215–340 nm. By scaling to σ(CH₃O₂)_{240 nm} = (4.24 ± 0.27) × 10^?18, the following absorption cross sections were determined: σ(HO₂)_{240 nm} = 1.29 ± 0.16, σ(C₂H₅O₂)_{240 nm} = 4.71 ± 0.45, σ(CH₃C(O)CH₂O₂)_{240 nm} = 2.03 ± 0.22, σ(CH₃C(O)CH₂O₂)_{230 nm} = 2.94 ± 0.29, and σ(CH₃C(O)CH₂O₂)_{310 nm} = 1.31 ± 0.15 (base e, units of 10^?18 cm² molecule^?1). To support the UV measurements, FTIR‐smog chamber techniques were employed to investigate the reaction of F and Cl atoms with acetone. The F atom reaction proceeds via two channels: the major channel (92% ± 3%) gives CH₃C(O)CH₂ radicals and HF, while the minor channel (8% ± 1%) gives CH₃ radicals and CH₃C(O)F. The majority (>97%) of the Cl atom reaction proceeds via H atom abstraction to give CH₃C(O)CH₂ radicals. The results are discussed with respect to the literature data concerning the UV absorption spectra of CH₃C(O)CH₂O₂ and other peroxy radicals. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 283–291, 2002     

THE EPR SPECTRA OF TETRADENTATE SCHIFF BASE COMPLEXES OF COPPER (II) I. N,N'-Bis-(acetylacetone) ethylenediimine and N,N'-Bis-(1,1,1-trifluoroacetylacetone) ethylenediimine

Abstract

The EPR spectrum of N, N'-bis-(acetylacetone)ethylenediimino Cu(II), [Cu-en(acac)₂], and N, N'-bis-(1,1,1-trifluoroacetylacetone)ethylenediimino-Cu(II), [Cu-en(tfacac)₂], have been studied in doped single crystals of the corresponding Ni(II) chelate. The parameters in the usual doublet spin-Hamiltonian are found to be: Cu[en(acac)₂], g_z =2.183 ± 0.003, g_x =2.047 ± 0.004, g_y =2.048 ± 0.004, A_z =204.8 × 10^?4cm^?1, A_x =31.5 × 10^?4cm^?1, A_y =27.1 × 10^?4 cm^?1, A_zN= 12.8 × 10^?4 cm^?1 and A_xN =A_yN =14.3 × 10^?4 cm^?1: Cu[en(tfacac)₂], g_z =2.192 ± 0.002, g_x =2.048 ± 0.004, g_y =2.046 ± 0.004, A_z =200.8 × 10^?4 cm^?1, A_x =31.1 × 10^?4 cm^?1, A_y =28.3 × 10^?4 cm^?1, A_zN =12.8 × 10^?4 cm^?1 and A_xN =A_yN =14.6 × 10^?4 cm^?1. These parameters are related to coefficients in the molecular orbitals of the complex. It is found that the α-bonding is quite covalent and there is significant in-plane σ-bonding. From the nitrogen hyperfine structure it is determined that the hybridization on the nitrogen is sp².     

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     

A new method for absolute absorption cross-section measurements: rhodamine-6G excited singlet-singlet absorption spectrum

A novel method is suggested to measure the absolute excited single-singlet absorption spectrum of rhodamine by bleaching completely the solution. The molar decadic extinction coefficient of the excited state (? = 4.8 × 10⁴ liter mole^?1 cm^?1 at 440 nm) is estimated directly from the plateau-like absorption signal at very high excitation intensities.     

UV-Absorption spectrum of the methylperoxy radical and the kinetics of its disproportionation reaction at 300 K

Molecular modulation spectroscopy combined with ultraviolet spectroscopic techniques have been used to observe the behavior of the CH₃O₂ radicals generated in the gas phase by near-ultraviolet modulated photolysis of flowing Cl₂? CH₄? O₂ mixtures. The kinetics of the disproportionation reaction (1) and the absorption cross-sections of CH₃O₂ were measured by computer fitting of the modulated absorption traces obtained in the wavelength range 220 to 270 nm at 300 K and 240 torr. The rate constant for the elementary self-reaction ??₁ = ??_1(a) + ??_1(b) + ??_1(c) was determined to be (3.61 ± 0.55) × 10_?13 cm³ molecule^?1 s^?1. The parameter ??_obs/σ (where ??_obs is the observed apparent second-order rate constant) was measured from the decay curves in the dark phase of the modulated photolysis period in the wavelength range 230–260 nm, and had a value 1.16 × 10⁵ cm² s^?1 at 250 nm. At 250 nm the absorption cross-section was determined as σ(CH₃O₂) = 4.14 × 10^?18 cm² molecule^?1, leading to a value of ??_obs, = (4.8 ± 0.5) × 10 ¹³ cm³ molecule^?1 s^?1. In addition, the absorption spectrum of CH₃O₂ was measured in the range 210–295 nm using diode array spectroscopy. A detailed review of all previous studies concerning the kinetics and spectrum of the CH₃O₂ radical is presented, and a recommended spectrum, representing an average from selected recent studies, is proposed.     

Rate constant of the gas-phase reaction between Fe atoms and CO2

The rate constant of the gas-phase reaction Fe(a ⁵ D ₄) + CO₂ at 1180–2380 K and a total gas density of (7.0–10.0) × 10^?6 mol/cm³ behind incident shock waves is k(Fe + CO₂) = 1.4 × 10^{14.0 ± 0.3}exp[?(14590 ± 1100)/T] cm³ mol^?1 s^?1, as determined by resonance atomic absorption photometry. Using thermochemical data available from the literature, the rate constant of the reverse reaction was calculated to be k(Fe + CO) = 9.2 × 10^{11.0 ± 0.3} (T/1000)^0.57exp[?(490 ± 1100)/T] cm³ mol^?1 s^?1. The results are compared with data reported earlier.     

Rate coefficients for the reactions of OH with n‐propanol and iso‐propanol between 237 and 376 K

The rate coefficients for the reaction OH + CH₃CH₂CH₂OH → products (k₁) and OH + CH₃CH(OH)CH₃ → products (k₂) were measured by the pulsed‐laser photolysis–laser‐induced fluorescence technique between 237 and 376 K. Arrhenius expressions for k₁ and k₂ are as follows: k₁ = (6.2 ± 0.8) × 10^?12 exp[?(10 ± 30)/T] cm³ molecule^?1 s^?1, with k₁(298 K) = (5.90 ± 0.56) × 10^?12 cm³ molecule^?1 s^?1, and k₂ = (3.2 ± 0.3) × 10^?12 exp[(150 ± 20)/T] cm³ molecule^?1 s^?1, with k₂(298) = (5.22 ± 0.46) × 10^?12 cm³ molecule^?1 s^?1. The quoted uncertainties are at the 95% confidence level and include estimated systematic errors. The results are compared with those from previous measurements and rate coefficient expressions for atmospheric modeling are recommended. The absorption cross sections for n‐propanol and iso‐propanol at 184.9 nm were measured to be (8.89 ± 0.44) × 10^?19 and (1.90 ± 0.10) × 10^?18 cm² molecule^?1, respectively. The atmospheric implications of the degradation of n‐propanol and iso‐propanol are discussed. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 10–24, 2010     

The Dependence on H2O and on NH3 of the Kinetics of the self-reaction of HO2 in the gas-phase formation of HO2·H2O and HO2·NH3 complexes

Electron pulse radiolysis at ?298°K of 2 atm H₂ containing 5 torr O₂ produces HO₂ free radical whose disappearance by reaction (1), HO₂ + HO₂ →H₂O₂ + O₂, is monitored by kinetic spectrophotometry at 230.5 nm. Using a literature value for the HO₂ absorption cross section, the values k₁ = 2.5×10^?12 cm³/molec·sec, which is in reasonable agreement with two earlier studies, and G(H) G(HO₂) ?13 are obtained. In the presence of small amounts of added H₂O or NH₃, the observed second-order decay rate of the HO₂ signal is found to increase by up to a factor of ?2.5. A proposed kinetic model quantitatively explains these data in terms of the formation of previously unpostulated 1:1 complexes, HO₂ + H₂O ? HO₂·H₂O (4a) and HO₂ + NH₃? HO₂·NH₃ (4b), which are more reactive than uncomplexed HO₂ toward a second uncomplexed HO₂ radical. The following equilibrium constants, which agree with independent theoretical calculations on these complexes, are derived from the data: 2×10^?20?K_4a?6.3 × 10^?19 cm³/molec at 295°K and K_4b = 3.4 × 10^?18 cm³/molec at 298°K. Several deuterium isotope effects are also reported, including k_H/k_D = 2.8 for reaction (1). The atmospheric significance of these results is pointed out.