Energy disposal in thermal-energy charge-transfer reactions: Ar+,Kr+ and Xe+ with NH3

Thermal-energy charge-transfer reactions from the ²P_3/2 state of Ar⁺, Kr⁺ and Xe⁺ with NH₃ are shown to be non-energy resonant: the kinetic energy released in each case has been measured, and the internal energy of the NH⁺₃ product ions deduced. Possible quenching of ²P_1/2 state of rare-gas ions in ICR cells is discussed.     

Direct observation of the spinorbit splitting in the Ar+ ion with a diode laser

The ²P_{$\text{1}\text{2}$}-²P_{$\text{3}\text{2}$} fine structure transition in the ground (3p⁵) state of the argon atomic ion. Ar⁺, has been detected in absorption using a tunable diode laser. The transition was calibrated against water vapour lines and measured to be 1431.644 ± 0.001 cm^?1 in ⁴⁰Ar⁺ and 3.0 × 10^?3 cm^?1 (91 MHz) smaller in ³⁶Ar⁺.     

Lifetimes and landé factors in the AOu+ and BO u+ states of 130Te2

Lifetimes and Landé factors were measured for rovibronic levels of the A O_u⁺ and B O_u⁺ states of ¹³⁰Te₂ excited by 514.5.496.5 and 488.0 nm Ar⁺-laser lines. Effective relaxation cross sections were obtained for collisions with ¹³⁰Te₂.     

The first synthesis, isolation and X-ray structure of a phosphonium phosphide, (Ph3PMe){[C6H2(CF3)3-2,4,6]2P}

The synthesis of a bulky secondary phosphine, Ar₂PH [Ar=C₆H₂(CF₃)₃-2,4,6], and its use in the first synthesis and isolation of a phosphonium phosphide, (Ph₃PMe)+(Ar₂P)⁻, via the deprotonation of Ar₂PH with a nonstabilised phosphorus ylide, Ph₃P=CH₂, are reported. An X-ray structure of this salt reveals that cations and anions are weakly associated in the solid state through C–HP interactions.     

Photoionization of the Ar2 dimer

The relative photoionization cross section for Ar₂ was measured in the wavelength region 820–860 Å. The spectrum shows detailed autoionization structure throughout this region with no contribution from direct ionization. The appearance potential of Ar⁺₂ corresponds to 856.5 ± 1.5 Å.     

C6F5XeF, a versatile starting material in xenon-carbon chemistry

The molecules Ar_FXeF (Ar_F=C₆F₅, 2,4,6-C₆H₂F₃) with a more polar Xe-F bond than XeF₂ are versatile starting materials for substitution reactions. Fluorine-aryl substitutions with Cd(Ar_F)₂, C₆F₅SiMe₃/[F]⁻, and C₆F₅SiF₃ formed symmetric and/or asymmetric diarylxenon compounds. Applying C₆F₅BF₂, with a higher F⁻-affinity than the corresponding aryltrifluorosilane, in contrast gave the salt [RXe] [Ar_FBF₃]. Using the alkenyl and alkyl compounds CF₂=CFSiMe₃/[F]⁻, CF₃SiMe₃/[F]⁻, and Cd(CF₃)₂ in reactions with C₆F₅XeF, the perfluoroalkenyl or -alkyl transfer reagents were consumed without observing C₆F₅XeCF=CF₂ or C₆F₅XeCF₃ but the formation of Xe(C₆F₅)₂ (dismutation product) and in the latter case C₆F₅CF₃ (coupling product), gave hints of the desired intermediates.     

Reductive elimination reaction of rhenium complexes trans-(η-C5Me5)Re(CO)2(chloroaryl)Cl

Thermal reaction of the chloroaryl-chloride complexes trans-(η⁵-C₅Me₅)Re(CO)₂(Ar^Cl)Cl (Ar^Cl = 3-ClC₆H₄, 3-ClC₆H₃(4-Me) and 3,5-Cl₂C₆H₃) in acetonitrile did not interconvert to the cis isomer, instead the complex ReCl(CO)₂(NCMe)₃ and the corresponding 5-Ar^Cl-1,2,3,4,5-pentamethylcyclopentadiene were formed. Similar reductive elimination products were obtained when the starting rhenium complexes were reacted with trimethylphosphite in toluene.     

Photodissociation of the dimer ions Ar+2, Ne+2, and (CO2)+2

The tandem quadrupole photodissociation mass spectrometer has been used to study photodissociation reactions of Ar⁺₂, Ne⁺₂, and (CO₂)⁺₂. The cross sections for photodissociation of Ar⁺₂ exhibited a strong dependence on ion source pressure, varying from 2 × 10 ^?18cm² at 0.1 torr to 6 × 10^?19cm² at 0.5 torr. A large photodissociation cross section (2 × 10^?17cm² for the reaction (CO₂)⁺₂ → CO⁺₂+ CO₂ was observed at the red end of the visible spectrum (580–620 nm) suggesting that this may be an important reaction in CO₂ rich planetary ionspheres such as that of Mars.     

Electronic nonadiabatic transitions in the reactive (Ar+ + H2, Ar + H+2, ArH+ + H) system. Numerical results for the collinear configuration

In this communication are presented exact quantum mechanical nonadiabatic electronic transition probabilities for the collinear reaction Ar⁺ + H₂(v_i = 0) → ArH⁺(v_f) + H. The calculations were performed using a potential surface calculated by the DIM method. It is established that large probabilities (≈ 1.0) can be obtained only if there is enough translational energy to overcome a potential barrier formed due to the crossing between v_i = 0 of the Ar⁺ + H₂ system and v_i = 2 of the Ar + H⁺₂ system. The threshold for the reaction is found to be 0.06 eV.     

Resonance raman spectra and quantum yields of MoS42−

Resonance Raman scattering of MoS₄^2? was studied in aqueous solution by irradiating its strong 4700 Å absorption band with five different lines of an Ar⁺ laser. The vibrational structure of the resonance spectra is discussed. Cross sections and quantum yields for the total scattered radiation were determined using NO₃^? as an internal standard.     

Electron-transfer and chemical reactivity following collisions of Ar with C2H2

The reaction between Ar²⁺ and C₂H₂ has been studied, at centre-of-mass collision energies ranging from 3 to 7 eV, using a position-sensitive coincidence technique to detect the monocation pairs, which are formed. Sixteen different reaction channels generating pairs of monocations have been observed, these channels arise from double-electron-transfer, single-electron-transfer and chemical reactions forming ArC⁺. Examination of the scattering diagrams and energetic information extracted from the coincidence data indicate that double-electron-transfer is a direct process, which does not involve a collision complex, and the derived energetics point towards a concerted, not stepwise, mechanism for the two-electron-transfer. As is commonly observed, single-electron-transfer from C₂H₂ to Ar²⁺ takes place via a direct mechanism, again not involving complexation. Most of the C₂H₂⁺ products that are formed in the single-electron-transfer reactions possess significant (12–15 eV) internal energy and fragment rapidly within the electric field of the partner Ar⁺ ion. The chemical reactions appear to proceed via a direct mechanism involving the initial formation of ArCH⁺, which subsequently fragments to form ArC⁺.     

Dynamics of SO(A3Π) formation in an argon + SO2 afterglow

The SO(A → X) fluorescence resulting from the Ar(³P_2,0)+SO₂ reaction has been studied in a flowing afterglow system. Various reaction pathways for the formation of the SO(A) fragment have been considered. A linear surprisal analysis of the vibrational distributions indicates that the resonance excitation with subsequent predissociation of the intermediate bound state is responsible for the formation of SO(A). A significant fraction of the available energy has been found to be partitioned into translation. Because the predissociation of SO₂ in the exit channel is dominating the reaction pathway in the Ar^*+SO₂ → Ar+O+SO(A) system, all the dynamical features can then be explained by the simple classical treatments on the dissociation of SO₂.     

X-ray photoelectron spectroscopy studies of Yb14MnSb11 and Yb14ZnSb11

Measurements of core and valence electronic states of single crystals of the rare earth transition metal Zintl phases Yb₁₄MnSb₁₁ and Yb₁₄ZnSb₁₁ were performed using the X-ray photoelectron spectroscopy station of Beamline 7 at the Advanced Light Source. Sample surfaces of Yb₁₄MnSb₁₁ and Yb₁₄ZnSb₁₁ were measured as received, after Ar⁺ ion bombardment, and after cleaving in situ. The single crystal structure of Yb₁₄ZnSb₁₁ is also reported. Both compounds are air-sensitive and show Yb³⁺ due to surface oxidation. In the case of Yb₁₄MnSb₁₁, there is no evidence for Yb³⁺ that would be intrinsic to the sample, consistent with previously reported X-ray magnetic circular dichroism studies. Detailed analyses of the Yb₁₄ZnSb₁₁ surfaces reveal a significant contribution of both Yb³⁺ and Yb²⁺ 4f states in the valence band region. This result is predicted for the Zn analog by Zintl counting rules and support the mixed valency of Yb for Yb₁₄ZnSb₁₁. Further detailed analysis of the core and valence band structure of both Yb₁₄MnSb₁₁ and Yb₁₄ZnSb₁₁ is presented.     

A flash photolysis study of the elimination of dinitrogen from trans-(N2)2W(dppe)2; dppe = 1,2-bis-diphenylphosphinoethane

Flash photolysis of trans-(N2)2W(dppe)2 (1) at ?60, ?30, ?10°C, and room temperature indicates that loss of dinitrogen occurs stepwise via the following proposed intermediates. Photodissociation of 1 gives the transient A decaying with k1 ～ 4450 s?1 to the doubly coordinatively unsaturated species [W(dppe)2], B. Further reactions of B are dependent on the type of gas used to saturate the solutions. In N2-saturated media, B is efficiently reconverted into the starting complex 1 via (N2)W(dppe)2], C(N2), kN22 = 450 s?1, which in turn takes up a second molecule of N2, kN23 = 3.7 s?1. In CO-saturated solutions, trans-(CO)2W(dppe)2 is produced as the final product and the corresponding rate constants are kCO2 1500 s?1 for B → C(CO) and kCO3 = 1.14 s?1 for C(CO) → product. In Ar-saturated solvents, B is transformed, again in two steps; kAr2 = 1 s?1 and kAr3 = 0.1 s1?, to products of unknown structure.The different rate constants kN22, kCO2, kAr2 and kN23, kCO3 and kAr3, together the common activation energy of ca. 11 kcal/mol?1 for the three processes A → B, B → C(N2) and C(N2) → 1 suggest that the reactions of B and C occur by SN2-type displacement of coordinated solvent molecules by the incoming ligands.     

Excitation of XeF* by reactions of XeF2 with Ar(3P0,2),Kr(3P2) and Xe(3P2)

The reactions of the lowest metastable states of Ar, Kr and Xe with XeF₂ were studied in a flowing afterglow apparatus; XeF emission (from D²Π_{$\text{1}\text{2}$} and B ²Π⁺ states) was observed in all cases. The total rate constants (cm³ molecule^?1 s^?1) for XeF^* formation were determined as 75 × 10^?11 ? Xe(³P₂);64 × 10^?11 ? Kr(³P₂) and 20 × 10^?11 ? Ar(³P_0,2). The reactions of Ar(³P_0,2) and Kr(³P₂) with XeF₂ also gave ArF^* and KrF^*, respectively. Analysis of these emissions indicates that at least two different mechanisms are operative: reactive quenching by the ionic—covalent curve-crossing mechanism and excitation transfer. The Ar(³P_0,2 + XeF₂ reaction is a sufficiently strong source of XeF(D—X) emission that the main features of the XeF(D²Π_{$\text{1}\text{2}$} ? X²Σ⁺) system could be photographed and tentative assignments of these vibrational bands are given. The XeF(D → B) emission could not be observed and the ratio of the D—X versus the D—B transition probability must be > 1000 : 1.     

Functionalization of Pentaphosphorus Cations by Complexation

The chemistry of polyphosphorus cations has rapidly developed in recent years, but their coordination behavior has remained mostly unexplored. Herein, we describe the reactivity of [P₅R₂]⁺ cations with cyclopentadienyl metal complexes. The reaction of [Cp^ArFe(μ‐Br)]₂ (Cp^Ar=C₅(C₆H₄‐4‐Et)₅) with [P₅R₂][GaCl₄] (R=iPr and 2,4,6‐Me₃C₆H₂ (Mes)) afforded bicyclo[1.1.0]pentaphosphanes ( 1‐R , R=iPr and Mes), showing an unsymmetric “butterfly” structure. The same products 1‐R were formed from K[Cp^Ar] and [P₅R₂][GaCl₄]. The cationic complexes [Cp^ArCo(η⁴‐P₅R₂)][GaCl₄] ( 2‐R [GaCl₄], R=iPr and Cy) and [(Cp^ArNi)₂(η^3:3‐P₅R₂)][GaCl₄] ( 3‐R [GaCl₄]) were obtained from [P₅R₂][GaCl₄] and [Cp^ArM(μ‐Br)]₂ (M=Co and Ni) as well as by using low‐valent “Cp^ArM^I” sources. Anion metathesis of 2‐R [GaCl₄] and 3‐R [GaCl₄] was achieved with Na[BArF₂₄]. The P₅ framework of the resulting salts 2‐R [BArF₂₄] can be further functionalized with nucleophiles. Thus reactions with [Et₄N]X (X=CN and Cl) give unprecedented cyano‐ and chloro‐functionalized complexes, while organo‐functionalization was achieved with CyMgCl.     

Raman and resonance-Raman spectra of CsI/I−3

Raman and resonance-Raman spectra of the I^?₃ ion isolated within CsI crystals have been studied using 647 nm and 488 nm exciting radiation. Sample temperatures between 300 and 20 K have been used. Eleven overtones of the symmetric stretching mode (nν₁) have been observed in the resonance-Raman spectrum excited by the 488 nm Ar⁺ laser line. Bands centred at 153, 170, 264 and 304 cm^?1 have been assigned as ν₃, 2ν₂, ν₁+ν₃ and 2ν₃(Σ⁺) respectively. The remaining structure between the nν₁ lines has been assigned as due to combinations of these lines with the lattice vibrations of the CsI crystal.     

Emission spectra of CH(A 2Δ) from methane in an argon flowing afterglow

The CH A ²ΔX²Π emission was observed in the flowing afterglow reaction of charged species of argon with CH₄. Energetic considerations show that metastable argon ions, Ar^+M(⁴D, ⁴F, ²F, ²G, are plausible candidates, although the contribution of Ar²⁺ cannot be completely excluded. The CH A ²ΔX²Π spectrum was analyzed; the ratio of vibrational populations for the υ′ = 0 and 1 states, P_vib(υ′ = 0), is estimated to be 0.56 ± 0.17, and the effective rotational temperatures are (3.0 ± 1.5) × 10³ and (1.7 ± 0.4) × 10³ K, respectively.     

[Ni(P2N2)2(NCMe)][BF4]2 as an electrocatalyst for H2 production: P2N2 = 1,5-(di(4-(thiophene-3-yl)phenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane)

A new cyclic 1,5-diaza-3,7-diphosphacyclooctane ligand was prepared with phenyl substituents on phosphorus and (thiophene-3-yl)phenyl substituents on nitrogen. This ligand reacts with [Ni(CH₃CN)₆][BF₄]₂ to form the corresponding [Ni(P^Ph₂N^Ar₂)₂(NCMe)][BF₄]₂ complex, 3, which is an active electrocatalyst for H₂ production. Kinetic studies indicate that the catalytic rate is first order in catalyst and second order in acid at low concentrations of acid, but at higher acid concentrations the catalytic rate becomes independent of acid concentration. The rate-determining step at high acid concentrations is attributed to the elimination of H₂ from a reduced Ni species. The modest overpotential of 280 mV and a turnover frequency of 56 s⁻¹ confirm that 3 is a relatively active catalyst for H₂ production in acetonitrile solutions. Oxidation of the pendant thiophene substituents of 3 results in the formation of films on glassy carbon electrode surfaces. However these films are not electroactive, and electrocatalysis of proton reduction is not observed with these modified electrodes.     

Ion spectroscopy of the N5+(4,0) meinel band using Ar charge exchange detection

The optical absorption spectrum of the transitions

has been observed in a flow tube by detection of the Ar⁺ product of the charge exchange reaction N₂⁺ + Ar → N₂ + Ar⁺. This reaction is fast for N₂⁺(A) Icvels, but very slow or zero for N₂⁺(X). The techinique is sensitive and applicable to the spectroscopic and reactive study of many ions.