Chemi-ionization reactions of photo-excited K atoms

Ion production resulting from excitation of K atoms to m²P (m ? 6) levels has been observed in mixtures of K with various species. Mass spectrometric data provide direct evidence for the occurrence of K(m²P) + K(4 ²S) → K₂⁺ + e^? and are consistent with the formation of unstable KX⁺ ions from K(m²P) + X → KX⁺ + e^? for X = C₂H₄, CH₄, N₂.     

Combination of metastable and ground-state mercury atoms into ungerade dimer states

The time evolution of the 2537 Å sensitised luminescence of mercury vapour has been examined at 304 K. With a trace of N₂ to generate Hg(6³P_o) and an excess of Ar to chaperon dimer formation, full time profiles of the ultraviolet and green bands have been recorded. The ultraviolet emission is of much shorter duration than the green with these gas mixtures. The reservoir of the ultraviolet band is the O^?_u state of the mercury dimer which correlates with Hg(6³P_o), Hg(6¹S_o) and is generated in the combination of metastable and ground-state mercury atoms. The Hg₂ O^?_u is efficiently relaxed to the O^±_g firstexcited states of the dimer in collision with Hg atoms, but rather inefficiently in collisions with Ar atoms. The rate coefficient for formation of excited trimers in the reaction Hg₂ O^±_g+ Hg(6¹S_o) + N₂ → Hg^*₃ + N₂ has been recorded as 1.95(±0.1) × 10^?30 cm⁶ molecule^?2s^?1 at 304 K.     

The interaction of metastable helium atoms with alkali atoms

Using crossed beams of ground state alkali atoms A (A = Li, Na, K, Rb, Cs) and metastable He(2³ S), He(2¹ S) atoms, we have measured the energy spectra of electrons resulting in the respective Penning ionization processes at: thermal collision energies. The data are interpreted to yield the well depthD _e ^* of the²Σ interaction potentials as follows: He(2³ S)+A:D _e ^* (A=Li)=868(20) meV;D _e ^* (Na)=740(25) meV;D _e ^* (K)=591(24) meV;D _e ^* (Rb)=546(18) meV;D _e ^* (Cs)=533(18) meV. He(2¹ S)+A:D _e ^* (Li)=330(17) meV;D _e ^* (Na)=277(24) meV;D _e ^* (K)=202(23) meV;D _e ^* (Rb)=219(18) meV;D _e ^* (Cs)=277(18) meV. The well depth for He(2³ S)+A(²Σ) is always close to 80% of the well depth for Li(2s)+A(X ¹Σ). The ionization cross sections for He(2¹ S)+A are about 3 to 4 times larger than those for He(2³ S)+A.     

Diatomics-in-molecules calculation of the potential energy surfaces relevant to penning ionization in the He(2 3S)H2 system

Potential energy surfaces and the autoionization width for the Penning ionization transition He(2 ³S) + H₂ → He + H⁺₂ + e^? have been calculated using the DIM method. The surfaces compare favourably with the existing ab initio calculations, and the approximation to the autoioinization width appear to be reasonable.     

Ground and first excited states of fractionally charged sodium atoms

The energy levels in sodium atoms with quarks attached to the nucleus are obtained using the configuration interaction method. It is found that the calculated 3p (²P) → 3s (²S) electronic transition in the Na^?1/3 quark–atom system is in agreement with that predicted by extrapolation of experimental data. Also, ionization potentials of fractionally charged sodium atoms are discussed. © 1993 John Wiley & Sons, Inc.     

The quantum theory of atoms in positronic molecules: A case study on diatomic species

This article presents the first systematic study of a series of diatomic positronic species using the recently proposed regional approach: the quantum theory of atoms in positronic molecules (QTAIPM). This survey includes the LiH,e⁺, NaH,e⁺, LiF,e⁺, NaF,e⁺, BeO,e⁺, MgO,e⁺, CN^?,e⁺, and OH^?,e⁺ species as typical examples. The computational algorithm of the whole analysis is communicated and reviewed in detail. The topological analysis of the joint density distribution reveals topological structures similar to those observed for the purely electronic systems; that is, each system decomposes into two quantum atoms. By considering some of the regional properties of these quantum atoms, it is demonstrated that the positron affects them seriously through two different mechanisms: direct and indirect contributions, the latter refers to electronic and geometric relaxations. The computational results clearly reveal the fact that the regional properties of the quantum atoms of positronic molecules are not deducible from their purely electronic counterparts; thus, an independent analysis is required for each positronic molecule. The positronic population is considered as a typical regional property showing that the attachment of a positron to a purely electronic system enhances the polarization of the electronic distribution. The concept of regional positron affinities is also introduced and discussed as a nonroutine application of the QTAIPM. The results of this article set the stage for further study on the quantum atoms of polyatomic positronic species. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Formation of oxygen atoms in the reaction of chlorine atoms with ozone

Oxygen atoms are detected by NO + O + M chemiluminescence as a secondary product of the reaction between Cl and O₃. The mechanism Cl + O₃ → ClO + O₂(¹Σ⁺_g), O₂(¹Σ⁺_g) + O₃ → O₂ + O₂ + O is proposed to account for the oxygen atom formation. The branching ratio to the O₂(¹Σ⁺_g) product in the reaction of Cl with O₃ is estimated to be in the range (0.1–0.5) x 10^?2.     

Collisional ionization of fast K atoms by H2S and D2S

The process K + H₂S/D₂S → HS^?/DS^? + K⁺+ H/D has been investigated for K impact energies from near threshold to ≈100 eV. Positive and negative ion energy spectra have been obtained in the forward direction. The threshold for HS^? or DS^?production corresponds to the HS^?/DS^?+ H/D limit of the ²A₁ H₂S^?/D₂S^? state at 1.55 eV.     

The interaction of metastable helium atoms with alkaline earth atoms: He*(23 S,21 S)+Mg,Ca, Sr and Ba

We have carried out experimental and theoretical studies of Penning ionization processes occurring in thermal energy collisions of state-selected metastable He*(2³ S) and He*(2¹ S) atoms with ground state alkaline earth atoms X(X=Mg, Ca, Sr, Ba). Penning ionization electron energy spectra for these eight systems, measured with a crossed-beam set-up perpendicular to the collision velocity at energy resolutions 40–70 meV, are reported; relative populations of the different ionic X ⁺ (ml) states are presented and well depths D*_e for the He*+X entrance channel potentials with uncertainties around 25 meV are derived from the electron spectra as follows: He*(2³ S)+Mg/Ca/Sr/Ba: 130/250/240/260 meV; He*(2¹ S) +Mg/Ca/Sr/Ba: 300/570/550/670 meV. The spectra show substantial differences for the three ionic states X ⁺(² S), X ⁺(² P) and X ⁺(² D) and reveal that transitions to a repulsive potential — attributed to He+X ⁺(² P)² Σ formation — are mainly involved for the X ⁺(² P) channel. Ab initio calculations of potential curves, autoionization widths, electron energy spectra and ionization cross sections are reported for the systems He*(2³ S)+Ca and He*(2¹ S)+Ca. The respective well depths D _e ^* are calculated to be 243(15) meV and 544(15) meV; the ionization cross sections at the experimental mean energy of 72 meV amount to 101 Ų and 201 Ų, respectively. Very good overall agreement with the experimental electron spectra is observed.     

The flash-photolysis of sodium pyrenide in tetrahydrofuran. On the photo-oxidation process and on the existence of sodium atoms NaO

Evidence is given that the yields of photo-oxidation for free pyrene anions (Π^?) and for anions associated with sodium cations (Π^?Na⁺) in liquid THF and THP are connected to the effective threshold values for the photo- ionization of free and associated pyrene anions. Our experimental results indicate that the phenomena observed by Fisher and Rämme after flash-photolysis of sodium pyrenide in THF which have led to the postulation of transient; sodium atoms Na⁰ may be interpreted as being caused by benzene or toluene negative ions.     

Charge transfer shake-up satellites in X-ray photoelectron spectra of solid compounds of 3d0 ions

Satellite structure has been observed at 8 eV and 12 eV below the main metal 2p peaks for compounds of Sc³⁺ and Ti⁴⁺. These features are attributed to charge transfer “shake-up”: transitions (t_2g → t_2g^* and e_g → e_g^* respectively). The 8 eV satellites are only found in sulphate complexes of Sc³⁺. This is the first observation of satellites which are probably due to t_2g → t_2g^* monopole charge transfer transitions. The probability for this transition is usually low, resulting in the observation of satellites due to the e_g → e_g transition.     

Associative ionization reaction N + O → NO<Superscript>+</Superscript> + e<Superscript>–</Superscript> in slow collisions of atoms

The endothermic associative ionization reaction N(²D) + O(³P) → NO** → NO(¹Σ⁺) +e^- in slow collisions of the atoms has been considered in terms of the multichannel quantum defect theory. The dependences of the partial and total cross sections of the reaction on the energy of the colliding atoms in the range of 0–0.3 eV have been calculated. It has been shown that the cross sections have a pronounced resonance structure, which is formed as a result of the multichannel interaction of autoionization states of the intermediate Rydberg complex NO** with dissociative states. The temperature dependence of the reaction rate constant is presented. The results are compared with those of other calculations and available experimental data.     

Theoretical study of spectroscopic parameters of alkali -Al and alkaline earth-Al dimers

The ground states of alkali-Al dimers (AlLi, AlNa, AlK, AlRb and AlCs) and alkaline earth-Al dimers (AlBe, AlMg, AlCa, AlSr and AlBa) along with their monovalent anions and cations were assigned based on the results of calculations. Bond lengths r _e , harmonic vibrational frequencies ω _e and dissociation energies D ₀ of these species were obtained. For neutral dimers, we also calculated adiabatic electron affinities (EA) and adiabatic ionization energies (IE). The present results are in agreement with the available experimental and other theoretical data. The ground state symmetry of AlLi, AlNa, AlK, AlRb and AlCs is ¹ Σ⁺. The ground state symmetry of AlBe⁺, AlMg⁺, AlCa⁺, AlSr⁺ and AlBa⁺ is also ¹Σ⁺. The ground state of AlLi^?, AlNa^?, AlK^?, AlRb^? and AlCs^? is ² Π, and is the same as in the isoelectronic neutral Al-alkaline-earth dimers. For both the alkali-Al and alkaline earth-Al neutral AlX species, the bond length increases monotonously with increasing atomic number of X. For the alkali-Al ions, energies of dissociation via the channels AlX^? → Al + X^? and AlX⁺ → Al + X⁺ are smaller than the energies of dissociation via the channel AlX^? → X + Al^? andAlX⁺ → X + Al⁺, respectively. While the opposite dissociation manner is found for alkaline earth-Al anions.     

Energy and polarization dependence of chemi-ionization processes inK(42 P 3/2)−K(42 P 3/2) collisions

Using crossed molecular beams we have investigated ionizing collisions between potassium atoms in their 4² P _3/2-states, leading to the exit channelsK ₂ ⁺ +e ^?,K ⁺+K ^?, andK(4² S _1/2)+K ⁺+e ^?, respectively. Measurements of the total ionization cross section as well as of the cross sections for the individual channels are reported as a function of both the relative collision energy (0.2 to 2.4 eV) and the angle between the electric field vector of the exciting laser light and the relative velocity vector. The results are interpreted in terms of the molecular states of theK ₂ ^* quasi molecule which are involved in the ionization process.     

The infrared chemiluminescent reaction of Cl atoms with H2CO

The reaction Cl + H₂CO → HCl + HCO has been studied at 295 K. Chlorine atoms were produced via the infrared laser induced dissociation of CCl₃F, using a pulsed CO₂ TEA laser. Using HCl infrared chemiluminescence as the diagnostic, we find the rate constant to be 7.4 ± 0.7 × 10^?11 cm³/molecule sec, in good agreement with several recent studies. An evaluation of TEA laser photolysis as a technique for the generation of chlorine atoms is made, and the relationship of this experiment to recent theories of infrared laser induced chemistry is discussed.     

EPR kinetic study of the reactions of F and Br atoms with H2CO

The absolute rate constants of the reactions F + H₂CO → HF + HCO (1) and Br + H₂CO → HBr + HCO (2) have been measured using the discharge flow reactor-EPR method. Under pseudo-first-order conditions (¦H₂CO¦?¦F¦or¦Br¦), the following values were obtained at 298 K: k₁ = (6.6 ± 1.1) × 10^?11 and k₂ = (1.6± 0.3) × 10^?12, Units are cm³ molecule^?1s^?1. The stratospheric implication of these data is discussed and the value obtained for k makes reaction (2) a possible sink for Br atoms in the stratosphere.     

b 1Σ+ Emissions from group V–VII diatomic molecules: bO+ → X1 O+ emission of Pl

Chemilluminescence of the bO⁺ → X₁O⁺ band system of P1 has been observed in a discharge flow system. Thirty-eight bands of the sequences, δν = +2, +1, 0, ?1, ?2 and ?3 were recorded photoelectrically at medium resolution. Evidence is presented that the vibrational numering assigned to the bands in the recently published first analysis of this system has to be modified. The re-analysis leads to the new constants (in cm ^?1) T_e = 11135 ± 5, ω′_e 400 ± 2, ω_e′_e = 1.4 ± 0.3, ω″_e = 372 ±2 and ωχ″_e, 1.4 ± 0.3 for the bO⁺ and χ₁ states, respectively. An upper limit of 0.01 was found for the ratio of the (0.0) band intensifies of the two sub-systems bO⁺ → χ₂ 1 and bO⁺ → χ₁O⁺.     

A Study of picosecond dehalogenation of chlorobenzene anions in liquids by positronium inhibition measurements

Radiation chemistry and results of Ps yields indicate that the following processes occur in the positron spur in solution of halogen-substituted hydrocarbons, RX_n: e⁺ + e^? → Ps, e^? + RX _n → (RX_n)^? → RX_n?1 + X^?, e⁺ + (RX_n)^? → Ps + RX_n, e⁺ + X^? → [X^?, e⁺]. Hence the trapped electron can form Ps only if (RX _n)^? is stable or has a lifetime that is longer than o comparable to the Ps formation time. Previous studies have shown that some of the strongly chlorinated benzenes (n = 4.5 give reasonable inhibition in benzene but not in linear hydrocarbons. The reason is very probably that the dechlorination time is much shorter in benzene than in saturated hydrocarbons because Cl^? is more strongly solvated in benzene than in non-aromatic hydrocarbons. To test those ideas further we have begun detailed studies of solutions of the possible “intermediate” inhibitors, viz. 1,2,3,5- and 1,2,4,5-C₆H₂Cl₄, in mixtures of C₆H₆/C₆H₁₄ different methyl-substituted benzene aniline, anisole, dioxane and ethylbenzene. The results are discussed and interpreted in terms of the spur model. The Ps inhibition efficiency of the two isomeric forms of tetrachlorobenzene studied, appears most probably to depend on intramolecular electron transfer with subsequent dehalogenation of the molecular anion on a picosecond timescale. The divergence in inhibitor efficiency obtained for the chlorobenzenes when dissolved in aromatic solvents compared to the same solutes when dissolved in a saturated alkane appears most probably to be caused by complex formation between the initially formed chlorobenzene anion and benzene molecules, which permits a rapid relaxation of the molecular anion with subsequent bond stretching and expulsion of the chloride anion.     

Generation and characterization of ionic and neutral methylene isothiocyanate by a combined tandem mass spectrometry and computational study

The heterocumulene, methyleneisothiocyanate ion, CH₂?N?C?S⁺ (1a⁺), is generated by the dissociative electron ionization of 2‐mercaptoimidazole. This conclusion follows from tandem mass spectrometry experiments and theoretical calculations at the B3LYP/6‐311G** and G2/G2(MP2) levels. The calculations predict that 1a⁺ is separated by high energy barriers from its isomers CHNCHS (1b⁺), CHNCSH (1d⁺), CNCHSH (1e⁺) and CHNHCS (1f⁺). The low energy metastable ions 1a⁺ dissociate by loss of HCN via the pathway 1a⁺ → 1b⁺ → HCS⁺ + HCN. Neutralization‐reionization experiments confirm the theoretical prediction that the hitherto unknown heterocumulene CH₂?N?C?S ^. is a stable species in the rarefied gas phase. Copyright © 2004 John Wiley & Sons, Ltd.