Vibrational state analysis of unrelaxed BaI from the reactions Ba + CH3I and Ba + CH2I2

The reactions Ba + CH₃I → BaI + CH₃ and Ba + CH₂I₂ → BaI + CH₂I have been investigated by the method of laser-induced fluorescence. Excitation spectra are reported for BaI products formed under single-collision conditions in a “beam-gas” arrangement. The production of BaI for Ba + CH₂I₂ is found to be a major reaction pathway with a cross section about twice that for Ba + CH₃I. The relative vibrational populations show for both reactions bell-shaped distributions peaking close to υ = 21 for Ba + CH₃I and υ = 39 for Ba + CH₂I₂. The corresponding average fraction of the total reaction exoergicity that appears as BaI vibration is $\text{f}$_υ = 0.18 for Ba + CH₃I and $\text{f}$_υ = 0.29 for Ba + CH₂I₂. In the case of Ba + CH₃I, an estimate for the average relative translational energy of the products, obtained from the primitive angular distribution measurements of Lin, Mims and Herm, can be combined with the average vibrational excitation of BaI to provide evidence that the internal excitation of the methyl radical exceeds that of BaI. A model is discussed which postulates an electron jump in the exit valley of the Ba + CH₃I reaction to account for this feature of the reaction dynamics.     

Monte Carlo simulation of O(1D) + H2 and O(1D) + HCl — rotational excitation of product OH radicals

Experimental studies with molecular beam and LIF techniques have independently shown that the reaction O(¹D) + H₂ → OH + H passes through a long-lived complex and gives products with small translational and large rotational excitation. We have previously published a statistical algorithm, based on ordinary RRKM theory with angular momentum restrictions included, which was designed to simulate molecular beam experiments. It has now been modified and applied to simulate the experimental rotational OH distributions from O(¹D)+H₂, measured by Luntz et al. The present study also includes simulation of similar results by Luntz for O(¹D) + HCI → OH + Cl. The purely statistical algorithm successfully simulates the apparently non-statistical experimental rotational distributions. For these reactions the total angular momentum conservation. which is applied at the transition state, proves to be decisive for the product energy distributions.     

Modified electron transfer model for excitation functions of the type M + RX → MX + R and M+ + RX− (M = alkali,R = alkyl group,X = halogen) and M′ + N2O → MO* + N2 (M′= Ba OR Sm)

A one-dimensional model is described for the excitation functions of reactions that are initiated by an electron transfer at close range. The process is governed by a barrier in the entrance channel, the abortive reflection of trajectories at higher energies and by the competition of an adiabatic and a diabatic channel for the reactive flux. The model is fitted to measured cross sections for the (K.Rb)+CH₃I, K+C₂H₅Br and (Ba.Sm)÷ N₂O reactions and the electron transfer cross section for K+CH₃I → K⁺ + CH₃I^- is successfully predicted from the fitting parameters of the reactive channel.     

Laser photoassociation of Xe and Br(2P3/2) atoms and generation of aligned XeBr(B) molecules

The laser-induced photoassociation of colliding pairs of Xe and Br(²P_3/2) atoms has been demonstrated by observing the XeBr(B→A) fluorescence following the XeBr(B→X) laser-induced excitation. Analysis of the B←X excitation spectrum shows that the excitation transition is almost entirely bound — free in nature. The fluore scence and excitation XeBr* spectra are used to discuss the XeBr (X, B and A) potentials. Analysis of the polarization of the XeBr(B-X) fluorescence shows that the XeBr(B) molecules are generated with a high degree of alignment relative to the plane-polarized laser beam. The pressure dependence of the decay rate of the total intensity and of the polarization give radiation lifetimes, quenching rate constants and an estimate for the de-alignment cross section in collisions with Xe.     

Optical spectroscopy of low-phonon Ho3+ doped BaY2F8 single crystal

The Ho:BaY₂F₈ crystal was grown by Czochralski method. The crystal phase structure and absorption spectra were tested, the absorption peak exists near 899 nm, the absorption cross section was 1.27 × 10^?21 cm². The emission spectra of crystals in the vicinity of 2 and 3.9 μm were measured, the 2 μm near infrared light induced by ⁵I₇ → ⁵I₈ transition of Ho3+ ions was observed, as well as the fluorescence output at 3.9 μm (⁵I₅ → ⁵I₆), emission cross section at 3.9 μm was calculated to be 0.86 × 10^?21 cm². We suppose that the Ho:BaY₂F₈ crystal has a large application prospect for the 2–4 μm wavelength near infrared laser.     

Chemiluminescence studies of vibrational-to-vibrational energy transfer: MF3 + HF

The vibrational-to-vibrational energy transfer process, MF³ + HF (ν = 0) → MF + HF³ (ν ? 9) is studied by means of a “triple beam” experiment. Vibrationally excited MF³ molecules are created at the intersection of crude crossed beams of M (M = Na, Mg) and F₂. The metal fluorides thus formed then cross an HF beam, where energy transfer occurs. This is observed by measuring the overtone emission from HF. Upper bounds on the reaction cross sections for M ÷ F₂ are measured to be 135 ± 20 A² for M = Na and 80 ± 15 A² for M = Mg, and laser induced fluorescence is used to determine the vibration energy distribution of MgF, which peaks at 2.6 eV. The chemiluminescence signal from the overtone emission indicates a large vibrational interconversion cross section, which is estimated to be ? 30 A².     

Reaction of excited iodine atoms with methyl iodide: Rate constant determinations

The rate constant for the reaction I(²P_1/2) + CH₃I → I₂ + CH₃ has been reevaluated taking into account both collisional deactivation of excited iodine atoms and loss of I₂ by I₂ + CH₃ → I + CH₃I. The reevaluation is based upon data obtained (R. T. Meyer), J. Chem. Phys., 46 , 4146 (1967) from the flash photolysis of CH₃I using time-resolved mass spectrometry to measure the rate of I₂ formation. Computer simulations of the complete kinetic system and a closed-form solution of a simplified set of the differential equations yielded a value of 6(± 4) × 10⁶ 1./mole-sec for the excited iodine atom reaction in the temperature region of 316 to 447 K. A slight temperature dependence was observed, but an activation energy could not be evaluated quantitatively due to the small temperature range studied. An upper limit for the collisional deactivation of I(²P_1/2) with CH₃I was also determined (2.4 × 10⁷ 1./mole-sec).     

The NO- and NO2-catalyzed decomposition of I2 in shock waves

Measurements of the NO-catalyzed dissociation of I₂ in Ar in incident shock waves were carried out in the temperature range of 700°-1520°K and at total concentrations of 5 × 10^?6-6 × 10^?5 mol/cm³, using ultraviolet-visible absorption techniques to monitor the disappearance of I₂. It was shown that the main reaction responsible for the disappearance under these conditions is I₂ + NO → INO + I, for which a rate coefficient of (2.9 ± 0.5) × 10¹³ exp[-(18.0 ± 0.6 kcal/mol)/RT] cm²/mol·sec was determined. The INO formed dissociates rapidly in a subsequent reaction. The reaction, therefore, constitutes a “chemical model” for a “thermal collisional release mechanism.” Preliminary measurements of the rate coefficient for I₂ + NO₂ → INO₂ + I are also presented. Combined with information on the reverse reactions obtained in earlier room temperature experiments, these results lead to accurate values of ΔH°_f for INO and INO₂ equal to 29.7 ± 0.5 and 15.9 ± 1 kcal/mol, respectively.     

Laser-induced fluorescence measurement of the vibrational distribution of CS formed in the reaction O + CS2 → CS + So

A frequency-doubled cw dye laser has been used to determine the initial vibrational distribution of CS formed in the reaction O + CS₂ → CS + SO by application of laser-induced fluorescence. The A¹5—X¹σ⁺ system of CS was excited, and rotationally resolved spectra of a number of bands measured. The vibrational distribution found for υ = 0–2 is 1.0:0.27:0.11, yielding a value of 6% for the fraction of reaction exoergicity entering vibration of this product. No evidence of high product rotational excitation wss detected for a reaction pressure 5 × 10^?3 Torr.     

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.     

Isomerization of 1,2-diiodoethylene in a laser-induced chemical reaction of I2 + C2H2

A laser-induced chemical reaction of I₂ + C₂H₂ has been studied and the formation of cis and tians isomers of 1,2-diiodoethylene has been observed. The ratio of the two isomers of 1,2-diodoethylene changes markedly upon changing the laser wavelengths of excitation of the I₂ molecule     

Pulsed,Crossed, Supersonic Molecular Beam Studies of Refractory Atom Reactions

Dynamics of refractory atom reactions have been studied with a crossed beam apparatus combining two pulsed, supersonic molecular beam sources, a pulsed UV laser for creating the refractory atoms in the gas phase by laser ablation, and a pulsed dye laser to probe the reaction products by laser-induced fluorescence. Examples of the A1(²P_j) + O₂(X³∑_g)→ A10(X²∑⁺) + O(³P_j), Mg(¹S_o) + N₂O(X¹∑⁺) → MgO(X¹∑⁺,a³Π) + N₂(X¹∑_g⁺) andC(³P_j) + NO(X²Π_r) → CN(X²∑⁺) + 0(³P_j) systems are given. Comparisons with the studies performed using the conventional steady-state beam approach are made.     

Kinetics of the reactions of CH3O with Br and BrO at 298 K

A discharge flow reactor coupled to a laser-induced fluorescence (LIF) detector and a mass spectrometer was used to study the kinetics of the reactions CH₃O+Br→products (1) and CH₃O+BrO→products (2). From the kinetic analysis of CH₃O by LIF in the presence of an excess of Br or BrO, the following rate constants were obtained at 298 K: k₁=(7.0±0.4)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹ and k₂=(3.8±0.4)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹. The data obtained are useful for the interpretation of other laboratory studies of the reactions of CH₃O₂ with Br and BrO. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 249–255, 1998.     

Quantum Mechanics Rate Constant for the N+ND Reaction

We present nonadiabatic quantum dynamical calculations on the two coupled potential en-ergy surfaces (1²A′ and 2²A′) [J. Theor. Comput. Chem. 8, 849 (2009)] for the reaction. Initial state-resolved reaction probabilities and cross sections for the N+ND→N₂+D reaction and N′+ND→N′D+N reaction for collision energies of 5 meV to 1.0 eV are determined, re-spectively. It is found that the N+ND→N₂+D reaction is dominated in the N+ND reaction.In addition, we obtained the rate constants for the N+ND→N₂+D reaction which demand further experimental investigations.     

Differential Cross Sections of F+HD→DF+H Reaction at Collision Energies from 3.03 meV to 17.97 meV

The prototypical reaction of F+HD→DF+H was investigated at collision energies from 3.03 meV to 17.97 meV using a crossed molecular beam apparatus with multichannel Rydberg tagging time-of-flight detection. Significant contributions from both the Born-Oppenheimer (BO) forbidden reaction F^*(²P_1/2)+HD→DF+H and the BO-allowed reaction F(²P_3/2)+HD→DF+H were observed. In the backward scattering direction, the contribution from the BO-forbidden reaction F^*(²P_1/2)+HD was found to be considerably greater than the BO-allowed reaction F(²P_3/2)+HD, indicating the non-adiabatic effects play an important role in the dynamics of the title reaction at low collision energies. Collision-energy dependence of differential cross sections (DCSs) in the backward scattering direction was found to be monotonously decreased as the collision energy decreases, which does not support the existence of resonance states in this energy range. DCSs of both BO-allowed and BO-forbidden reactions were measured at seven collision energies from 3.03 meV to 17.97 meV. It is quite unexpected that the angular distribution gradually shifts from backward to sideway as the collision energy decreases from 17.97 meV to 3.03 meV, suggesting some unknown mechanisms may exist at low collision energies.     

Energy dependence of the total reaction cross section for Br− + CH4

The energy dependence of the total cross section for the reaction Br^? + CH₄ → CH₂Br^? + H₂ was measured in a beam experiment. From the threshold energy it can be assumed that the above reaction proceeds via the same transition state as the nucleophilic substitution leading to the also observed H^?. Thus we propose Br^? + CH₄ → [CH₄Br^?]

     

Energy Migration Upconversion in Manganese(II)‐Doped Nanoparticles

We report the synthesis and characterization of cubic NaGdF₄:Yb/Tm@NaGdF₄:Mn core–shell structures. By taking advantage of energy transfer through Yb→Tm→Gd→Mn in these core–shell nanoparticles, we have realized upconversion emission of Mn²⁺ at room temperature in lanthanide tetrafluoride based host lattices. The upconverted Mn²⁺emission, enabled by trapping the excitation energy through a Gd³⁺ lattice, was validated by the observation of a decreased lifetime from 941 to 532 μs in the emission of Gd³⁺ at 310 nm (⁶P_7/2→⁸S_7/2). This multiphoton upconversion process can be further enhanced under pulsed laser excitation at high power densities. Both experimental and theoretical studies provide evidence for Mn²⁺ doping in the lanthanide‐based host lattice arising from the formation of F^? vacancies around Mn²⁺ ions to maintain charge neutrality in the shell layer.     

Notiz zur Kenntnis der roten Monohalogenide des Indiums,InX (X = CI,Br, I)

Inhaltsübersicht. Synthese (aus den Elementen; Einkristalle durch Sublimation im Gradienten: 200 → 100°C) und Strukturverfeinerung von InI (orthorhombisch, Cmcm, Z = 4; a = 476,3(1); b = 1278,1(1); c = 490,9(1) pm) werden beschrieben. Ein Vergleich mit InBr und InCl (alle TlI-Typ) weist auf die Bedeutung des 5s²-Elektronenpaares von In⁺ für diesen Strukturtyp und auf attraktive Wechselwirkungen in Richtung auf die Ausbildung eines Dimeren, In₂²⁺, hin. Note on the Red Monohalides of Indium, InX (X = CI, Br, I) Synthesis (from the elements; single crystals by sublimation in a 200 → 100°C gradient) and structure refinement of InI (orthorhombic, Cmcm, Z = 4, a = 476.3(1), b = 1278.1(1), c = 490.9(1) pm) are reported. A comparison with the isotypic halides InBr and InCl (all TlI type) hints at the importance of the 5s² electron pair of In⁺ for this structure type. Attractive interactions in the direction of the formation of a dimer, In₂²⁺, could play a role.     

A violet emission from optically excited mercury vapour. Kinetics of the formation and decay of excited dimers and trimers

A new electronic systems has been observed from excited Hg vapour, which is assigned to collisionally induced emission from the Hg₂ O^±_g first excited states of the dimer: Hg₂O^±_g + M → 2Hg(6 ¹S₀) + M + hv(γ_max 3950 A). For M = N₂, the rate coefficient is 5.3(±0.7) × 10^?19 cm³ molecule^?1 at 298 K. From time resolved measurements of the luminescence in the afterglow following pulsed excitation, the decay rate of the green emission, in an excess of N₂, is shown to be a linear function of [Hg][N₂]. It is concluded that the reaction which controls the decay of the excitation is formation of an excited trimer in a termolecular reaction; the trimer is the carrier of the green emission: Hg₂ O^±_g + Hg(6 ¹S₀ + Hg(6¹S₀ + N₂ → Hg₃³Π_u + N₂. The rate coefficient is 1.10(±0.07) × 10^?30 cm⁶ molecule^?2 s^?1 at 298 K.     

Emission spectrum and formation kinetics of neon fluoride

The emission spectrum and the formation kinetics of NeF* is studied using two different excitation techniques. Bye-beam excitation of a Ne/F₂ mixture the yield was found to be low having a maximum at 0.2 hPa of F₂ and at a low neon pressure of less than 0.2 MPa. An ion exchange reaction between Ne⁺ and RbF leading to NeF* was initiated by irradiation of a mixture of neon and RbF vapor using an argon-ion beam. TheD →X transition of NeF* was observed at 107.0 nm, theB →X transition at 108.8 nm. The kinetics of the reactions are discussed.