The quenching of excited iodine atoms by oxygen molecules as studied by opto-acoustic spectroscopy

The opto-acoustic spectrum of I₂ in the presence of various quenching gases — NO, O₂, CH₃I, SO₂, C₃H_S, N₂, and He — has been studied. Of these, the I₂/O₂ spectrum is quite different due to the near-resonant energy transfer I(²P$\text{1}\text{2}$) + O₂(³Σ) → I(²P$\text{3}\text{2}$) + O₂(^IΔ), wherein the resistance of the O₂((^IΔ) species to collisional relaxation severely distorts the acoustic signal. The photochemical production of excited ²P$\text{1}\text{2}$ iodine atoms commences at wavelengths considerably longer than the dissociation limit of the I₂B? state.     

Matrix IR studies on hydrogen-bonded complexes of hydrogen chloride and hydrogen bromide with ketene

Infrared spectra of matrices codeposited Ar/HX (X=Cl, Br) with Ar/H₂CCO mixtures have been examined. Isotopic substitutions (HX, DX, H₂CCO, D₂CCO) showed that ketene formed the 1:1 hydrogen-bonded complex with HX. The HX stretching modes were observed at 2684 cm⁻¹ in the H₂CCO–HCl complex and at 2384 cm⁻¹ in the H₂CCO–HBr complex. The ν₁ modes of the ketene submolecules were shifted to low frequency and the ν₉ modes to high frequency. It was proposed for the structure of the complex that the acid proton is bonded to the C=C pi electron system.     

Uranyl ion-sensitized polymerization of acrylamide and methacrylamide in aqueous solution

The kinetics of polymerization of the vinyl monomers, acrylamide and methacrylamide, photosensitized by uranyl ions in homogeneous aqueous acid medium was studied systematically. Monochromatic radiation of wavelengths 365, 405, and 436 mμ was used for irradiation. Uranyl perchlorate in aqueous perchloric acid (pH = 0–2) was used as the sensitizer to ensure that only uncomplexed UO₂²⁺ ions existed in the solution. Polymerization was found to proceed without any induction period, the steady state being attained in about 10–20 min., and was followed by the measurement of the rate of monomer disappearance by bromine addition method. The chain lengths of the polymers were determined by viscometry. It was observed that there was no change in the initiator concentration, [UO₂²⁺], during polymerization. The dependence of the rate of polymerization on variables like light intensity, light absorption fraction by the active species, wavelength, monomer concentration, hydrogen ion concentration, temperature, nature of the acid used (HClO₄ and H₂SO₄), viscosity of the medium etc., were studied. A kinetic reaction scheme is proposed and discussed in the light of the experimental results. Certain rate parameters were calculated. The mechanism of photosensitization by uranyl ions with specific reference to primary photochemical act, initiation of polymerization etc., are discussed.     

A theoretical study of the condensation reactions of methyl cation with ammonia,water, hydrogen fluoride and hydrogen sulphide

Ab initio molecular orbital calculations have been used to study the condensation reactions of CH₃^? with NH₃, H₂O, HF and H₂S. Geometry optimization has been carried out at the Hartree—Fock (HF) level with the split-valence plus d-polarization 6-31G* basis set and improved relative energies obtained from calculations which employ the split-valence plus dp-polarization 6-31G** basis set with electron correlation incorporated via Moller—Plesset perturbation theory terminated at third order (MP3). Zero-point vibrational energies have also been determined and taken into account in deriving relative energies. The structures of the intermediates CH₃XH^? (X = NH₂, OH, F and SH) have been obtained and dissociation of these intermediates into CH₂X⁺ + H₂ on the one hand, and CH₃^? + HX on the other, has been examined. It is found that for those species for which the methyl condensation reaction is observed to have an appreciable rate (X = NH₂ and SH), the transition structure for hydrogen elimination from CH₃XH^? lies significantly lower in energy than the reactants CH₃^? + HX (by 75 and 70 kJ mol^?1 respectively). On the other hand, for those species for which the methyl condensation reaction is not observed (X = OH and F), the transition structure for H₂ elimination lies higher in energy than CH₃^? + HX (by 6 and 87 kJ mol^?1 respectively).     

Hydrogen abstraction by fluorine atoms: F + HX and F + DX (X = I,Br, Cl)

Absolute reaction rates for F + HX and F + DX (X = I, Br, Cl) have been obtained by monitoring the rise time of HF (DF) vibrational fluorescence following multiphoton dissociation of SF₆ in mixtures of HX (DX) and argon. The cross sections for reaction are, in units of 10^?16 cm², 4.37, 5.26, and 1.16 for HI, HBr, and HCl, respectively. The isotope effects k_HX/k_DX, are 1.29 ± 0.14, 1.29 ± 0.18, and 1.38 ± 0.29, respectively.     

Photoinitiated free radical polymerization of vinyl compounds in aqueous solution

A new method for the photochemical initiation of polymerization of vinyl compounds in aqueous solution is described. The photochemically active species is an ion pair complex of the formula Fe³⁺X⁻(X⁻ = OH⁻, CI⁻, N⁻₃, etc.). The light absorption by the ion pair leads to an electron transfer causing reduction of the cation and oxidation of the anion to an atom or free radical X. The latter leads to the initiation of polymerization in accordance with X + CH₂CHR→XCH₂ CHR . The kinetics of the reaction were studied by the measurement of: (a) ferrous ion formed (colorimetrically), (b) monomer disappearance (by titration and by weighting the polymer), (c) the chain length of the polymer (in the case of methyl methacrylate). The dependence of the quantum yield on the light intensity, light absorption fraction, and the concentration of vinyl monomer and ferrous ion added initially was investigated. A complete mechanism, both with regard to the formation of free radicals and the polymerization reaction, was put forward involving: (1) light absorption, (2) a primary dark back reaction, (3) dissociation of the primary product, (4) a secondary dark back reaction, (5) initiation of polymerization by free radicals, (6) propagation of polymerization, and (7) termination by recombination of active polymer endings. The mechanism was verified by the experimental results and some constant ratios were estimated quantitatively.     

The heavier pnictogen and chalcogen analogues of isocyanic and cyanic acids and their dimers: A high level ab initio study

The CCSD(T)/cc-pVTZ//CCSD/cc-pVTZ method is used to determine the geometries and energetics of the isomers HXCY vs HY─CX (XN, P, As; YO, S) and their dimers from chain dimerizations and head-to-head or head-to-tail [2 + 2] cyclodimerizations. The HO─CX structures with CX triple bonds lie at energies at least 18.5 kcal/mol above their HXCO isomers. However, the energy differences between the HXCS and HS─CX isomers are found to be particularly small, especially in the [H,P,C,S] and [H,As,C,S] systems. For (HNCY)₂, the lowest energy dimers are the chain isomers, which lie ~11 kcal/mol below the lowest energy cyclic dimers aNO containing a NCNC ring and cNS containing a NCSC ring. Formation of the remaining dimers through dimerization from two monomers is predicted to be endothermic and thus thermodynamically disfavored. However, the energies of the chain isomers in the other (HXCY)₂ (XP, As; YO, S) series are higher than those of the corresponding isomeric lowest energy cyclodimers. For (HXCO)₂ (XP, As), the lowest energy structures are the head-to-head dimers hPO and hAsO containing a C─C─XX ring. For (HXCS)₂ (XP, As), the lowest energy structures are the head-to-head dimers gPS and gAsS with a CCXS ring.     

Potential energy distributions and normal coordinates of methyl,methyl-d3 and partially deuterated methyl chloride,bromide and iodide

The potential energy distributions and normal coordinates (L^?1 matrices) for twelve methyl halides, CH₃X, CH₂DX, CD₂HX and CD₃X (X = Cl, Br, I) have been calculated from known structural data. General harmonic force fields for methyl chloride, bromide and iodide previously determined from the most complete available isotopic frequency, Coriolis and centrifugal distortion data were used. The vibrational modes of these molecules are compared and discussed.     

Mass spectrometry of organic compounds of the group V Elements: VI—A new type of amine fragmentation under electron impact

A new type of amine fragmentation under electron impact is elucidated for proline, sarcosine and aspartic acid derivatives and aminomethylphosphines of the general formula R₂NCH₂X. Ordinary α-cleavage affording the \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}_2 \mathop {\rm N}\limits^{\rm + } {\rm = CH}_{\rm 2} $\end{document} ion is suppressed by elimination of a neutral HX particle and [M - HX]⁺ ion formation, or M-HX neutral particle ejection and generation of an [HX]⁺ ion from [M]⁺˙. Such fragmentation is ensured by the presence of an α-heteroatom (N, O, P, S) in one substituent (X) and a CO₂R type delocalizing group in the α-position of the other substituent (R₂N).     

Anomaly in dispersion intermolecular potential produced by intense radation field

It is predicted that a gap of 2μE/3^{$\text{1}\text{2}$} appears in the dispersion potential for a pair of ground-state (identical) atoms, or molecules, at distance R such that ?δ + (4π?₀)^?1($\text{μ}{}^2\text{3}\text{R}{}^3$)(1 ? 3 cos²θ) = 0, where μ is the electric dipole moment, E is the field strength of an intense radiation field and θ is the angle between the polarization direction of the field and R. The detuning term Δ is ω₀?ω where ω₀ is the transition frequency of the atom or molecule, and ω is that of the field. The gap is of the order of 10¹¹ Hz when the intensity of the radiation field is a few $\text{MW}\text{cm}{}^2$.     

Simulated ion trajectory and induced signal in ion cyclotron resonance ion traps. Effect of ion initial axial position on ion coherence,induced signal,and radial or z ejection in a cubic trap

The effects of ion initial axial position on coherence of ion motion, induced ion cyclotron resonance (ICR) signal. and radial and z ejection have been evaluated by numerical simulation for a cubic Fourier transform-ion cyclotron resonance ion trap. For a given initial ion cyclotron phase and radius, ions of different initial z position are shown to be excited to significantly different ion cyclotron radii (and ultimately radially ejected at significantly different excitation amplitude-duration products). Ion initial z displacement from the trap midplane affects observed ICR signal magnitude in two ways: (1) for the same postexcitation cyclotron radius, an ion with larger initial z displacement induces a smaller ICR signal and (2) an ion with larger initial z displacement is excited to a smaller cyclotron radius. We also evaluate the induced ICR signal as a function of excitation amplitude-duration product for spatially uniform or Gaussian ion initial z distributions. In general, if the excitation waveform contains components at frequency, 2 ω_z or (ω₊ + 2 ω_z, in which ω_z is the axial C“trapping”) oscillation frequency, then ejection occurs axially. However, the resulting excitation amplitude-duration product for such axial ejection is significantly higher (factor of, ～ 4) than that required for radial ejection (at ω₊) for ions of small initial radius. The present results offer the first explanation of how, even if the ion is initially at rest on the z axis (i.e., zero excitation electric field amplitude on the z axis), z ejection (axial ejection) may nevertheless occur if the excitation waveform contains frequency components at ω₊ + 2ω_z and/or 2_{w z} Namely, our simulations reveal that off-resonant excitation pushes ions away from the z axis, after which the ions are exposed to z excitation and eventual z ejection.     

On the kinetic stability of the SH3X species with X=F,Cl

Portions of the [S, H₃, X] (X=F, Cl) potential energy surfaces (PESs) were explored using the RHF, MP2, and QCISD(T) methods with emphasis on H₂ and HX eliminations, SH₃X→SHX+H₂ and SH₃X→SH₂+HX, respectively. Upon the halogen X substitution, the most favorable decomposition pathway of SH₄ went over to HX elimination, proceeding with a very low activation barrier of 6.9 (X=F) and 1.3 (X=Cl) kcal/mol. Moreover, the transition states (TSs) for H₂ elimination from SH₃X resembled the less favorable homopolar TS of SH₄. Upon the X=F substitution, the barrier to H₂ loss of SH₄ was calculated to increase from 19.5 to 21.5 kcal/mol. For X=Cl, only the indirect H₂ elimination path via the SH₂+HCl→SHCl+H₂ exchange was found. The hydrogen‐exchange reaction SH₂+HX→SH₂+HX was predicted to occur through formation of the hydrogen‐bonded complex XHSH₂ and with a relatively high barrier of 43.5 (X=F) and 38.5 (X=Cl) kcal/mol. FHSH₂ and ClHSH₂ were found to be the lowest energy species on the [S, H₃, F] and [S, H₃, Cl] PESs, lying 53.4 and 44.7 kcal/mol below SH₃F and SH₃Cl, respectively. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 73: 37–43, 1999     

A highly variable opto-acoustic phase angle within the So → S1 band of glyoxal

The S₀ → S₁ transition in the opto-acoustic spectrum of glyoxal vapor exhibits a variable phase angle which follows the pattern of absorption intensity. This unusual phenomenon results from a quenching of T₁ by S_o to form a long-lived intermediate, M, which then produces heat via an M + M reaction.     

The mechanism and kinetics of energy transfer processes in Xe–CCl4–M (M=CO,CO2) mixtures irradiated by xenon resonance light

The mechanism and kinetics of energy transfer from the Xe(6s[3/2]₁) resonance state to CO and CO₂ molecules have been investigated by XeCl(B–X) (λ_max=308 nm) fluorescence intensity measurements at stationary conditions in Xe–CCl₄–M systems. Steady-state analysis of the fluorescence intensity dependence on the xenon and M pressure at constant CCl₄ concentration shows that these processes occur in two- and three-body reactions: Xe(6s[3/2]₁⁰)+M→products; Xe(6s[3/2]₁⁰)+M+Xe→products. The two-body rate constants for above reactions have been found to be (0.7±0.2)×10⁻¹⁰ and (4.9±0.4)×10⁻¹⁰ cm³ s⁻¹ for CO and CO₂, respectively. The three-body rate constants have been found to be (3±1)×10⁻²⁹ and (2.4±0.3)×10⁻²⁸ cm⁶ s⁻¹ for CO and CO₂, respectively. It has been shown that the third order reaction is a very effective channel of xenon excited atoms decay at high xenon pressures (P(Xe)>50 Torr).     

Why Are B ions stable species in peptide spectra?

Protonated amino acids and derivatives RCH(NH₂)C(+O)X · H⁺ (X = OH, NH₂, OCH₃) do not form stable acylium ions on loss of HX, but rather the acylium ion eliminates CO to form the immonium ion RCH = NH ₂ ⁺ . By contrast, protonated dipeptide derivatives H₂NCH(R)C(+O)NHCH(R′)C(+O)X · H⁺ [X = OH, OCH₃, NH₂, NHCH(R″)COOH] form stable B₂ ions by elimination of HX. These B₂ ions fragment on the metastable ion time scale by elimination of CO with substantial kinetic energy release (T _1/2 = 0.3–0.5 eV). Similarly, protonated N-acetyl amino acid derivatives CH₃C(+O)NHCH(R′)C(+O)X · H⁺ [X = OH, OCH₃, NH₂, NHCH(R″)COOH] form stable B ions by loss of HX. These B ions also fragment unimolecularly by loss of CO with T _1/2 values of ～ 0.5 eV. These large kinetic energy releases indicate that a stable configuration of the B ions fragments by way of activation to a reacting configuration that is higher in energy than the products, and some of the fragmentation exothermicity of the final step is partitioned into kinetic energy of the separating fragments. We conclude that the stable configuration is a protonated oxazolone, which is formed by interaction of the developing charge (as HX is lost) with the N-terminus carbonyl group and that the reacting configuration is the acyclic acylium ion. This conclusion is supported by the similar fragmentation behavior of protonated 2-phenyl-5-oxazolone and the B ion derived by loss of H-Gly-OH from protonated C₆H₅C(+O)-Gly-Gly-OH. In addition, ab initio calculations on the simplest B ion, nominally HC(+O)NHCH₂CO⁺, show that the lowest energy structure is the protonated oxazolone. The acyclic acylium isomer is 1.49 eV higher in energy than the protonated oxazolone and 0.88 eV higher in energy than the fragmentation products, HC(+O)N⁺H = CH₂ + CO, which is consistent with the kinetic energy releases measured.     

Chemiluminescence of NS radical produced by the reaction of active nitrogen with sulfur vapor and sulfur chloride

Kinetics of NS (B² Π → X²Π) emission produced by the reaction of active nitrogen with sulfur vapor or sulfur chloride (S₂Cl₂) has been studied as a function of the total pressure and of the concentrations of atomic nitrogen and sulfur. The B ²Π state of NS is selectively formed by the three-body recombination reaction of N ans S atoms, N(⁴S) + S(³P) + M →. NS(B ²Π) + M. The highest vibrational level of the B ²Π state observed is ν′ = 12, which gives a lower bound for the dissociation energy of 4.93 eV.     

The role of orbiting collisions in vibrational energy transfer

Using a simple model of molecular collisions under a spherically symmetric interaction, it is shown that orbiting collisions can make very large contributions to the inelastic cross sections of non-resonant processes. Calculations for the system HX + CO₂(001) → HX(υ=1) + CO₂(000), where X = F, Cl, I show good agreement with experimental results.     

Synthesis of Silver Complexes in DMSO–HX and DMSO–HX–Ketone Systems

Comparative analysis of the oxidizing and complexing properties of the DMSO–HX (X = Cl, Br, I) and DMSO–HX–ketone (X = Br, I; the ketone is acetone, acetylacetone, or acetophenone) systems toward silver was performed. The reaction products are AgX (X = Cl, Br, I), [Me₃S⁺]Ag _n X^– _m (n= 1, 2; m= 2, 3; X = Br, I) and [Me₂S⁺CH₂COR]AgX^– ₂(R = Me, Ph; X = Br, I). The composition of the obtained complexes depends on both the DMSO : HX ratio and the nature of HX, as well as on the methods used to isolate solid products from the solution. It was noted that the formation of the [Me₂S⁺CH₂COMe]AgBr^– ₂complex in the Ag⁰–DMSO–HBr–acetylacetone system occurs with cleavage of the acetylacetone C–C bond and follows a specific reaction course. The optimum conditions for production of the silver compounds in the title systems are determined.     

Chemical ionization and collisional activation spectra of α,β-unsaturated nitriles

A study of the chemical ionization (CI) and collisional activation (CA) spectra of a number of α, β-unsaturated nitriles has revealed that the even-electron ions such as [MH]⁺ and [MNH₄]⁺ produced under chemical ionization undergo decomposition by radical losses also. This results in the formation of M ⁺˙ ions from both [MH]⁺ and [MNH₄]⁺ ions. In the halogenated molecules losses of X˙ and HX compete with losses of H˙ and HCN. Elimination of X˙ from [MH]⁺ is highly favoured in the bromoderivative. The dinitriles undergo a substitution reaction in which one of the CN groups is replaced with a hydrogen radical and the resulting mononitrile is ionized leading to [M ? CN + 2H]⁺ under CI(CH₄) or [M ? CN + H + NH₄] and [M ? CN + H + N₂H₇]⁺ under CI(NH₃) conditions.     

The Structural Systematics of Protonation of Some Important Nitrogen‐base Ligands. I Some Univalent Anion Salts of Doubly Protonated 2, 2′:6′, 2″‐Terpyridyl

A number of salts of 2,2′:6′,2″ ‐terpyridyl (‘tpy’) with univalent anions (halides : X = Cl, Br, I; oxyanions of increasing basicity: ClO₄, NO₃, ‘tfa’ = trifluoroacetate, ‘tca’ = trichloroacetate), variously solvated, have been structurally characterized by single crystal X‐ray studies. In all cases the tpy moieties are found to be doubly protonated [tpyH₂]²⁺, the hydrogen atoms being associated with the nitrogen atoms of the peripheral rings, these together with the central nitrogen atom being directed towards a common focus, in most cases ‘chelating’ one of the counter‐ion components in diverse ways. Thus the chloride and bromide compounds are isomorphous [(tpyH₂)X]⁺X⁻·H₂O arrays; a second dihydrate phase is also described for the chloride, the two forms having the unchelated anion and water molecules engaged in hydrogen‐bonded networks essentially independent of [(tpyH₂)X]⁺. The iodide is anhydrous, and of a different structural type, the anions, presumably too large for chelation, lying out of plane to either side, and linking different cations into a one‐dimensional polymer; in the perchlorate, the unsolvated aggregate is now discrete [(tpyH₂)X₂], a pair of perchlorate ions disposed to either side of the tpy plane, lying each with one oxygen atom interacting with both of the two protonating hydrogen atoms. In the anhydrous X = NO₃, tfa, tca arrays, the lattices are solvated by the parent acids; one oxygen atom of each anion is chelated by the [tpyH₂]²⁺ as in the chlorides, the other anion, with the acid, forming an independent ‘acid salt’ counterion [XHX]⁻ in each case, retaining the additional protonic hydrogen rather than further protonating the central ring, all being of the form [(tpyH₂)X]X·HX = [(tpyH₂)X][X(HX)].