Observation of a possible pure electric quadrupole transition in solid Cs2NaSmCl6

A no-phonon transition has been observed in Cs₂NaSmCl₆ at 6355 cm^?1. This transition is assigned, in octahedral symmetry, as E″_u(⁶H_{$\text{5}\text{2}$}) → E'_u(⁶F_{$\text{1}\text{2}$}) and is proposed to be of pure electric quadrupole origin. A comparison between the experimental and calculated intensity and the orientation-dependent intensity of an associated vibronic transition lend support to this assignment.     

Yields of O2(1Σg+) and O2(1Δg) in the H + O2 reaction system,and the quenching of O2(1Σg+) by atomic hydrogen

The generation of metastable O₂(¹Σg⁺) and O₂(¹Δg) in the H + O₂ system of reactions was studied by the flow discharge chemiluminescence detection method. In addition to the O₂(¹Σg⁺) and O₂(¹Δg) emissions, strong OH(v = 2) → OH(v = 0), OH(v = 3) → OH(v = 1), HO₂(²A′₀₀₀) → HO₂(²A″₀₀₀), HO₂(²A′₀₀₁) → HO₂(²A″₀₀₀), and H O₂(²A″₂₀₀) → HO₂(²A″₀₀₀) emissions were detected in the H + O₂ system. The rate constants for the quenching of O₂(¹Σg⁺) by H and H₂ were determined to be (5.1 ± 1.4) × 10^?13 and (7.1 ± 0.1) × 10^?13 cm³ s^?1, respectively. An upper limit for the branching ratio to produce O₂(¹Σg⁺) by the H + HO₂ reaction was calculated to be 2.1%. The contributions from other reactions producing singlet oxygen were investigated.     

Experimental determination of the rate constants of the reactions of HO2 + DO2 and DO2 + DO2

The rate constants of the reactions of DO₂ + HO₂ (R1) and DO₂ + DO₂ (R2) have been determined by the simultaneous, selective, and quantitative measurement of HO₂ and DO₂ by continuous wave cavity ring-down spectroscopy (cw-CRDS) in the near infrared, coupled to a radical generation by laser photolysis. HO₂ was generated by photolyzing Cl₂ in the presence of CH₃OH and O₂. Low concentrations of DO₂ were generated simultaneously by adding low concentrations of D₂O to the reaction mixture, leading through isotopic exchange on tubing and reactor walls to formation of low concentrations of CH₃OD and thus formation of DO₂. Excess DO₂ was generated by photolyzing Cl₂ in the presence of CD₃OD and O₂, small concentrations of HO₂ were always generated simultaneously by isotopic exchange between CD₃OD and residual H₂O. The rate constant k₁ at 295 K was found to be pressure independent in the range 25–200 Torr helium, but increased with increasing D₂O concentration k₁ = (1.67 ± 0.03) × 10⁻¹² × (1 + (8.2 ± 1.6) × 10⁻¹⁸ cm³ × [D₂O] cm⁻³) cm³ s⁻¹. The rate constant for the DO₂ self-reaction k₂ has been measured under excess DO₂ concentration, and the DO₂ concentration has been determined by fitting the HO₂ decays, now governed by their reaction with DO₂, to the rate constant k₁. A rate constant with insignificant pressure dependence was found: k₂ = (4.1 ± 0.6) × 10⁻¹³ (1 + (2 ± 2) × 10⁻²⁰ cm³ × [He] cm⁻³) cm³ s⁻¹ as well as an increase of k₂ with increasing D₂O concentration was observed: k₂ = (4.14 ± 0.02) × 10⁻¹³ × (1 + (6.5 ± 1.3) × 10⁻¹⁸ cm³ × [D₂O] cm⁻³) cm³ s⁻¹. The result for k₂ is in excellent agreement with literature values, whereas this is the first determination of k₁.     

The importance of spin relaxation in the delayed fluorescence of molecular crystals

Deactivation rate constants of spin-orbital excited Br atoms in the reactions Br(²P_{$\text{1}\text{2}$}) + O₂ → Br(²P_{$\text{3}\text{2}$}) + O₂ (k₁), and Br(²P_{$\text{1}\text{2}$}) + NO → Br(²P_{$\text{3}\text{2}$}) + NO (k₄) have been measured with a photodissociative IBr laser on the electronic transition ²P_{$\text{1}\text{2}$}?²P_{$\text{3}\text{2}$} in the Br atom (λ = 2.7 μm). The values obtained are (6.4 ± 1.8) × 10^?14 cm³ s^?1 and (1.9 ± 0.6) × 10^?12 cm³ s^?1, respectively. Comparison with published data leads to the conclusion that, contrary to a widely accepted point of view, the high rate constants for the quenching of excited halogen atoms are due to resonant energy transfer processes and not to the paramagnetic nature of the quencher.     

Absolute rate constants for the self reactions of HO2, CF3CFHO2, and CF3O2 radicals and the cross reactions of HO2 with FO2, HO2 with CF3CFHO2, and HO2 with CF3O2 at 295 K

The kinetics of the self-reactions of HO₂, CF₃CFHO₂, and CF₃O₂ radicals and the cross reactions of HO₂ with FO₂, HO₂ with CF₃CFHO₂, and HO₂ with CF₃O₂ radicals, were studied by pulse radiolysis combined with time resolved UV absorption spectroscopy at 295 K. The rate constants for these reactions were obtained by computer simulation of absorption transients monitored at 220, 230, and 240 nm. The following rate constants were obtained at 295 K and 1000 mbar total pressure of SF₆ (unit: 10⁻¹² cm³ molecule⁻¹ s⁻¹): k(HO₂+HO₂)=3.5±1.0, k(CF₃CFHO₂+CF₃CFHO₂)=3.5±0.8, k(CF₃O₂+CF₃O₂)=2.25±0.30, k(HO₂+FO₂)=9±4, k(CF₃CFHO₂+HO₂)=5.0±1.5, and k(CF₃O₂+HO₂)=4.0±2.0. In addition, the decomposition rate of CF₃CFHO radicals was estimated to be (0.2–2)×10³ s⁻¹ in 1000 mbar of SF₆. Results are discussed in the context of the atmospheric chemistry of hydrofluorocarbons. © 1997 John Wiley & Sons, Inc.     

Some comments on vibronic intensities of naphthalene fluorescence spectra from single vibronic levels

It is shown that some features of intensity distribution among certain vibronic transitions in naphthalene molecule can be understood, when one takes into account adiabatic and nonadiabatic interaction between S₁(¹B_3u), S₂(^tB_2u), and S₃(^IB_3u) electronic states. the vibronic activity of the $\text{6}\text{?}$(b_1g) mode in naphthalene-d₈ can be explained in terms of an anharmonic coupling with the $\text{7}\text{?}$(b_1g) mode. The theoretical analysis suggests reinterpretation of some vibronic transitions.     

The reaction of nitric oxide with vibrationally excited ozone

The reaction between nitric oxide and vibrationally excited ozone was studied in a fast flow reactor by monitoring the visible emission from electronically excited NO₂¹. The antisymmetric mode (ν₃) of O₃ was excited with a Q-switched 9.6 μm CO₂ laser, and a laser-induced signal was detected, with a rise rate constant of (4.0 ± 0.5) × 10¹¹ cm³/mole sec and a decay rate constant of (1.1 ± 0.1) × 10¹¹ cm³/mole sec for an NO-rich mixture. The latter was unaffected by addition of large amounts of He or Ar, indicating that the signal was not a thermal effect. Most of the measurements were made at 350°K; however, the He and Ar dilution results suggest that the enhanced reaction rate is not very sensitive to temperature. In order to explain the observed rise times, it was necessary to postulate an intermediate step prior to the chemical reaction. A model which is consistent with our data has energy transferred from ν₃ to ν₂ (the bending mode) at a rate of (2.9 ± 0.5) × 10¹¹ cm³/mole sec for NO and a rate of (1.1 ± 0.2) × 10¹¹ cm³/mole sec for He. According to this model, the rate constant for the reaction of NO with O₃ (ν₂= 1) producing vibrationally excited ground state NO₂²,

$\text{NO + O}{}_3{}^2\text{(010)}\text{3}\text{NO}{}_2{}^2\text{+ O}{}_2$

is (1.5 ± 0.2) × 10¹¹ cm³/mole sec, and the relative rate for the reaction of O₃ (ν₂ = 1) and O₃(ν₂ = 0) with NO was estimated to be $\text{k}{}_3\text{(1)}\text{k}{}_3\text{(0)}\text{≈ 22}$.     

On the decay of the ozonide radical in aqueous alkaline solutions

In flash photolysis of an oxygenated aqueous potassium persulphate solution at pH 12.5 the decay of the ozonide radical has been found to follow $\text{3}\text{2}$ order kinetics which has been explained by reactions O^?₃ + O^? ? 2 O^?₂ and O^?₃ + HO₂ → 2 O₂ + OH^?     

Fluorescence quantum yields and cascade-free lifetimes of state selected CO+2, COS+, CS+2 and N2O+ determined by photoelectron—photon coincidence spectroscopy

The details and principles of an apparatus built for measurements of fluorescence quantum yields and cascade-free lifetimes of open-shell cations are reported. These rely on the detection of coincidences between energy selected photoelectrons and undispersed photons. The results of such measurements for CO⁺₂, COS⁺, CS⁺₂ and N₂O⁺ in selected vibrational levels of their excited states are presented. Non-unity fluorescence quantum yields are found for some vibronic levels of CO⁺₂($\text{B}$), COS⁺ ($\text{A}$), N₂OP⁺($\text{A}$) and a non-exponential decay is observed for CS⁺₂($\text{A}$). The data yield the following values for the radiative lifetimes: CO⁺₂($\text{A}$) 124 ± 6 ns, CO⁺₂($\text{B}$) 140 ± 7 ns, COS⁺($\text{A}$) 550 ± 50 ns and N₂O⁺($\text{A}$) 240 ± 12 ns.     

Kinetics and mechanism of the reaction of Cl atoms with HO2 radicals

The kinetic and mechanism of the reaction Cl + HO₂ → products (1) have been studied in the temperature range 230–360 K and at total pressure of 1 Torr of helium using the discharge‐flow mass spectrometric method. The following Arrhenius expression for the total rate constant was obtained either from the kinetics of HO₂ consumption in excess of Cl atoms or from the kinetics of Cl in excess of HO₂: k₁ = (3.8 ± 1.2) × 10^?11 exp[(40 ± 90)/T] cm³ molecule^?1 s^?1, where uncertainties are 95% confidence limits. The temperature‐independent value of k₁ = (4.4 ± 0.6) × 10^?11 cm³ molecule^?1 s^?1 at T = 230–360 K, which can be recommended from this study, agrees well with most recent studies and current recommendations. Both OH and ClO were detected as the products of reaction (1) and the rate constant for the channel forming these species, Cl + HO₂ → OH + ClO (1b), has been determined: k_1b = (8.6 ± 3.2) × 10^?11 exp[?(660 ± 100)/T] cm³ molecule^?1 s^?1 (with k_1b = (9.4 ± 1.9) × 10^?12 cm³ molecule^?1 s^?1 at T = 298 K), where uncertainties represent 95% confidence limits. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 317–327, 2001     

Lifetimes of the vibronic Ã2A1 states of H2S+

Lifetimes have been measured for the Σ and Π vibronic òA₁ states of H₂S⁺ by studying the decay curves of the òA₁ (0, υ′₂, 0) → X? ²B₁ (0, υ″₂, 0) emission bands. The vibronic òA₁ states are produced via excitation of H₂S molecules by 150 eV electrons. The Σ sublevels 1 ? υ′₂ ? 7 and the Π sublevels 3 ? υ′₂ ? 6 have been considered. Predissociation occurs in the Σ sublevels for υ′₂ ? 7 and in the Π sublevels for υ′₂ ? 6. The obtained radiative lifetimes for the non-predissociated Σ and Π sublevels are around 4.2(±0.4) × 10^?6 s and 5.6(±0.5) × 10^?6 s respectively. For the predissociated Σ(0, 7, 0) and Π(0, 6, 0) levels the corresponding lifetimes are 2.3(±0.3) × 10^?6 s and 1.6(±0.3) × 10^?6 s respectively. The rate constant for collisional deactivation (quenching) of the vibronic òA₁ states by H₂S molecules was found to equal 2.3(±0.3) × 10^?9 cm³ mol^?1 s^?1.     

Direct observation of the ν6 band in the IR spectrum of CF3I dissolved in liquid xenon

The IR spectrum of CF₃I dissolved in liquefied xenon at 185 K shows a very weak peak at 265.2 cm^?1 due to the ν₆ fundamental vibration. The separation, $\text{ν}$₃  $\text{ν}$₆, 19.3 cm^?1 is the same as that deduced from the microwave spectrum of CF₃I in the gas phase.     

Determination of D0o(BaI) from the chemiluminescent reaction Ba + I2

A study is made of the visible chemiluminescence resulting from the reaction of an atomic beam of barium with I_Z under single-collision conditions (～ 10^?4 torr). The resulting spectrum consists of the BaI C²Π → X²Σ emission on top of an underlying “continuum”. The variation of the BaI emission intensity with Ba and I₂ flux is investigated, and it is concluded that the reaction is bimolecular. The total phenomenological cross section for barium atom removal is determined to be 86 A², which agrees well with the total reactive cross section calculated assuming an electron jump mechanism. The short wavelength cutoff is identified as the transition from the υ′ = 41 level of the BaI C²Π_{$\text{3}\text{2}$} state to the υ′ = 41 level of the BaI X²Σ state. A strict lower bound D^o₀(BaI) ? 102 ± 0.7 kcal/mole for the ground state dissociation energy of BaI is obtained from this short wavelength cutoff. The value D^o₀(BaI) = 102 ± 1 kcal/mole is recommended, where the error estimate includes the possible contribution from the final relative translational energy of the products.     

Observation of new bands in the N2 Herman infrared system and kinetic study of its formation in a pulsed-discharge apparatus

Four new bands of the unassigned N₂ Herman infrared system (HIR) are observed in a pulsed-discharge apparatus. The upper HIR state is produced by the N₂(A) + N₂(A) energy pooling reaction which is studied by time-resolved spectroscopy; its production rate constant is found to be ?4 × 10^?11 cm³ molecule^?1 s^?1 and its energy $\text{}\text{?}$12eV.     

Emission spectra of supersonically cooled methyldiacetylene cations

The ā²E → X?²E (Σ= + $\text{1}\text{2}$, - $\text{1}\text{2}$) electronic transitions of rotationally/vibrationally cooled CH₃CCCCH^- cation, as well as the d₁-/d₃-/d₄-substituted species, were studied by emission spectroscopy. Ion emission was obtained by electron impact on the neutral species seeded in a helium supersonic free jet. Vibrational frequencies in both electronic states are inferred to within ±1 cm^-1. Spin-orbit splittings are observed and interpreted on the basis of non-linear vibronic couplings. Rotational subbands are observed, yielding rotational and Coriolis parameters as well as rotational temperatures.     

Herpetetradione,nouveau lignoide tetramere isole d'Herpetospermum caudigerum wall.

The title compound, a new tetramer of coniferyl alcohol, has been isolated from seeds of $\text{Herpetospermum caudigerum}$ Wall. (Cucurbitaceae). Its structure was elucidated by spectroscopic means as $\text{rel}$-(7′S, 8′S, 7″S, 8″)-4,9,4′,4″,4″′,9″′-hexahydroxy-5,5′5″,5″′-tetramethoxy-7,7″′-dioxo-8.3′, 7′.0.9″,8′.8″,9′.0.7″,3″.8″′ -lignoïd.     

b 1Σ+ emissions from group V-VII diatomic molecules: bo+ → X10+, X21 emissions of SbBr

Chemiluminescence studies of the reactions of microwave-discharged oxygen with SbBr₃ have led to the observation of some band sequences in the near infrared region which are attributed to b0⁺ → X₁0⁺ and b0⁺ → X₂1 transitions of SbBr. Analysis of the spectra yielded T_e values for the X₂1 and b0⁺ states of 874 ± 10 and 12756 ± 10 cm^?1, respectively, and vibrational frequencies in the X₁0⁺, X₂1 and b0⁺ states of ω′'_e(X₁, X₂) = 257 ± 10 and ω′_e(b) = 270 ± 10cm^?1.     

An FTIR study of the Cl-atom-initiated reaction of glyoxal

The kinetics and mechanism of Cl-atom-initiated reactions of CHO? CHO were studied using the FTIR detection method to monitor the photolysis of Cl₂–CHO? CHO mixtures in 700 torr of N₂–O₂ diluent at 298 ± 2 K. The observed product distribution in the [O₂] pressure of 0–700 torr combined with relative rate measurements provide evidence that: (1) the primary step is Cl + CHO? CHO → HCl + CHO? CO with a rate constant of [3.8 ± 0.3(σ)] × 10^?11 cm³ molecule^?1 s^?1; (2) the primary product CHO? CO unimolecularly dissociates to CHO and CO with an estimated lifetime of ≤ca. 1 × 10^?7 s; (3) alternatively, the CHO? CO reacts with O₂ leading to the formation of CO, CO₂, and most likely the HO radical, but no stable products containing two carbon atoms; (4) the HO₂ radical, formed in the secondary reaction CHO + O₂ → HO₂ + CO, reacts with the CHO? CHO with a rate constant ca. 5 × 10^?16 cm³ molecule^?1 s^?1 to form HCOOH and a new transient product resembling that detected previously in the HO₂ reaction with HCHO.     

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.     

Errata

The π → π* absorption spectrum of thioformaldehyde has been recorded at relatively high pressures and path lengths. The system is quite extensive and in H₂CS displays a progression of bands in an interval of 476cm^?1 which can be followed out to ν′ = 12. This is assigned to the ν′₃ CS stretching mode. A second weaker set of bands is assigned to 2ν′₄ the out-of-plane bending mode. The 725 cm^?1 interval observed here compared to the 711 cm^?1 value of the ã state leads us to the conclusion that the barrier to inversion is less than 50 cm^?1.