Level-to-level vibrational energy transfer studies: energy dependence and observation of product species for azulenes(S0, Evib) + CO2

V—V energy transfer from a large molecule excited to vibrational energies of chemical interest has been demonstrated by detection of ≈ 1.5% yield of CO₂(001) due to energy transfer from azulene (E_vib ≈ 30600 cm^?1. Also, the average enery lost per collision by azulene was measured as a function of E_vib, and the rate constant for CO₂(001) deactivation by azulene was determined.     

Preferential energy transfer from N2(A) to specific energy levels of Cu atoms

Emission spectra resulting from reaction of “clean” N₂(A³ Σ_u⁺) with copper atoms were studied using a flowing afterglow apparatus. The population distribution of the Cu states was calculated from the spectrum; it indicates that Cu atoms are excited by nearly resonant energy transfer processes. N₂(A,v') + Cu(²S_{$\text{1}\text{2}$}) → N₂(X, v) + Cu^* , and that the transfer is most efficient for N₂(A,v') → N₂(X,v) transitions with large Franck-Condon factors. The preferential energy transfer results in population inversion between some of the Cu states.     

Molecular beam chemiluminescence XI: kinetic and internal energy dependence of the NO + O3 → NO2*,→ NO23 reaction

Seeded supersonic NO beams were used to study the kinetic energy dependence of both the electronic (NO₂^*) and vibrational (NO₂³) chemiluminescence of the NO + O₃ reaction. In addition the electronic CL is found to be enhanced by raising the NO internal temperature. This is shown to be due to enhanced reactivity of the NO(²Π,_{$\text{3}\text{2}$}) fine structure component. By difference NO(²Π_{$\text{1}\text{2}$}) is concluded to yield predominantly groundstate NO₂³. The excitation function for NO₂^* formation from NO(²Π_{$\text{3}\text{2}$}) is of the form σ_{$\text{3}\text{2}$}(E) = C(E/E₀ - 1)ⁿ over the 3–6 kcal energy range where n = 2.4 ± 0.15, C = 0.163 Ų and E₀ = 3.2 ± 0.3 kcal/mole. Vibrational IR emission from NO₂³ has an energy dependence different from electronic NO₂^* emission, confirming that emitters are formed predominantly in distinct reaction channels rather than via a common precursor (either NO₂^* or NO₂³). The short wavelength cutoff of the CL spectra recorded at elevated collision energies E ? 15 kcal/mole corresponds to the total available energy. These and literature results are discussed in the light of general properties of the (generally unknown) ONO₃ potential energy surfaces. The formation of electronically excited NO₂^* rather than energetically preferred O₂ (¹ Δg) (Gauthier and Snelling) can be rationalized in terms of surface hopping near a known intersection of potential energy surfaces more easily than by vibronic interaction in the asymptotic NO₂ product.     

Double (n=2) and triple (n=3) [M4Bi2n−2O2n] polycationic ribbons in the new Bi∼3Cd∼3.72M∼1.28O5(PO4)3 oxyphosphate (M=Co, Cu, Zn)

The crystal structure of the new Bi_∼3Cd_∼3.72Co_∼1.28O₅(PO₄)₃ has been refined from single crystal XRD data, R₁=5.37%, space group Abmm, a=11.5322(28) Å, b=5.4760(13) Å, c=23.2446(56) Å, Z=4. Compared to Bi_∼1.2M_∼1.2O_1.5(PO₄) and Bi_∼6.2Cu_∼6.2O₈(PO₄)₅, this compound is an additional example of disordered Bi³⁺/M²⁺ oxyphosphate and is well described from the arrangement of double [Bi₄Cd₄O₆]⁸⁺ (=D) and triple [Bi₂Cd_3.44Co_0.56O₄]⁶⁺ (=T) polycationic ribbons formed of edge-sharing O(Bi,M)₄ tetrahedra surrounded by PO₄ groups. According to the nomenclature defined in this work, the sequence is TT/DtDt, where t stands for the tunnels created by PO₄ between two subsequent double ribbons and occupied by Co²⁺. The HREM study allows a clear visualization of the announced sequence by comparison with the refined crystal structure. The Bi³⁺/M²⁺ statistic disorder at the edges of T and D entities is responsible for the PO₄ multi-configuration disorder around a central P atom. Infrared spectroscopy and neutron diffraction of similar compounds (without the highly absorbing Cadmium) even suggests the long range ordering loss for phosphates. Therefore, electron diffraction shows the existence of a modulation vector q^*=1/2a^*+(1/3+ε)b^* which pictures cationic ordering in the (001) plane, at the crystallite scale. This ordering is largely lost at the single crystal scale. The existence of mixed Bi³⁺/M²⁺ positions also enables a partial filling of the tunnels by Co²⁺ and yields a composition range checked by solid state reaction. The title compound can be prepared as a single phase and also the M=Zn²⁺ term can be obtained in a biphasic mixture. For M=Cu²⁺, a monoclinic distortion has been evidenced from XRD and HREM patterns but surprisingly, the orthorhombic ideal form can also be obtained in similar conditions.     

Production of electronically excited atoms. H + Br2 → HBr + Hb(*), H + HBr → H2 + Br(*)

By measurement of infrared chemiluminescence we have obtained for the branching ratio of the room temperature reaction H + Br₂ (1), k*₁/k₁ = 0.015 ± 0.004 and for H + HBr (2), k*₂/k₂ ? 0.013. For H + Br₂ → HBr(υ^· ? 6) + Br (1), the detailed rate constant k(υ^* = 6) = 0.014 ± 0.003 relative to k(υ^· = 4) = 100.     

Attachment of NH3 clusters to Hg(6P0)

The ultraviolet luminescence from the Hg-photosensitised reaction of ammonia was investigated at pressures up to 10 atmospheres. From a variation of the wavelength distribution on the [NH₃], it was concluded that Hg(6³P₀) can attach clusters of NH₃ molecules to form Hg(NH₃)_n^* with n up to at least 5. The emission profiles of the stabilized complexes with n = 1–4 were determined, and also the profile from unstabilised HgNH₃^* formed in a bimolecular encounter of Hg(6³P₀) with NH₃. Dissociation constants for complexes with n = 2, 3 and 4 were measured.     

The T3 (π, π) State of acridine

The 00 band maximum of the transition T₃(π, π^*) ← T₁ (π, π^*) of acridine occurs at ≈ 10200 ± 20 cm^?1 in inert (n-hexane, benzene, CCl₄), at 10220 ± 20 cm^?1 in polar (acetonitrile) and at 10170 ± 50 cm^?1 in hydrogen-bonding (methanol, 2-propanol and alkaline water) solvents. Based on the solvent-independent energy of T₁ (π, π^*), the T₃(π, π^*) state of acridine is estimated at 26050 ± 50 cm^?1 in all the solvents.     

Diffusion coefficient measurement of O*2(1Δg) in ground state O2

The diffusion coefficient of O_*2(¹Δ_g) in O₂(³Σ^?_g) has been measured as a function of pressure, D^* = 0.201 ± 0.005 cm² s^?1 at 1 atmosphere and 298 K.     

Translational energy distributions and production mechanisms of the excited hydrogen atom (n = 3,4) produced in e-NH3 collisions

The Balmer α and β lines produced in e-NH₃ collisions have been measured precisely with the use of a Fabry-Perot interferometer. These lines are not polarized. The translational energy distributions of (H^*(n = 3,4) were determined from analysis of Doppler lineshapes and have five components; their peaks lie at 1, 3, 2, 4–5 and 8–12 eV. The excitation function [H^*(n = 4)] has five thresholds at 22.5, 29.0, 33.3, 38.9 and 41.7 eV, and indicates that five dissociation processes contribute to the formation of H^*. Excitation to the Rydberg states converging to the (2a₁)^?1 state of NH₃⁺ is a major process for the formation of the first and the second components. Doubly excited Rydberg states play important roles in the dissociative excitation of NH₃.     

Fluorescence spectra and intramolecular vibrational redistribution in jet-cooled perylene

The jet-cooled fluorescence spectra of perylene excited to the S₁ state with E_vib = 0–1600 cm^?1 are recorded and analyzed. For E_vib <800 cm^?1 only the resonant fluorescence was detected. Ground- and excited-state frequencies of 14 low-frequency normal modes are determined. A drastic change in frequency of the “butterfly” modes upon electronic excitation shows that perylene slightly deviates from planarity in its ground state and is more rigid in the excited singlet state. For a number of levels in the E_vib = 800–1600 cm^?1 range, the fluorescence is composed of the resonant emission and of non-resonant (“‘relaxed’”) bands. It is shown that apparently single bands in the fluorescence-excitation spectrum correspond to ovelapping bands pumping different molecular eigenstates resulting from the intrastate coupling. The relative role of the anharmonicity and of the Coriolis interaction are discussed. The data are treated in terms of a selective coupling between doorway and hallway states with the coupling constant rapidly decreasing with the difference in the overall vibrational quantum number between initial and final state.     

On the relationship between the structures of Cu(II) complexes and their chemical transformations

The experimental activation energies (E ^*) of dehydration of Cu(NH₃)₄(H₂O)SO₄, Cu(en)₂(H₂O)X₂ (X=Cl^?, Br^?), Cu(en)(H₂O)₂SO₄, Cu(py)₂(H₂O)₂SO₄, CuCl₂ · 2H₂O and M ₂ ^I CuCl₄ · 2H₂O (M ^I =NH₄, K, Rb) were obtained from their non-isothermal thermogravimetric curves using the Coats-Redfern method. TheseE ^* values were compared with known data on the structures of the Cu(II) coordination polyhedra in the above complexes. No dependence of theE ^* values was found on either the central atom — released ligand bond length, or the number and lengths of the hydrogen bonds formed by the released water molecules. However, it was found that it is justified to seek some relationship between theE ^* values and the anisotropic temperature factors of the donor atoms of the ligands split off.     

Quenching of the Ba + Cl2 chemiluminescence: Estimate of BaCl*2 radiative lifetime

The chemiluminescence produced by the Ba + Cl₂ reaction was recorded as a function of He and N₂ pressure. A modified Stern-Volmer treatment of competitive electronic quenching of BaCl^* and BaCl^*₂ emission yielded upper limits to the half pressures p_{$\text{1}\text{2}$}(He) ? 9.0 ± 3 mtorr and p_{$\text{1}\text{2}$} (N₂) ? 1.1 ± 0.2 mtorr for quenching of BaCl^*₂ by helium and nitrogen, respectively. A lower limit of the BaCl^*₂ radiative lifetime is placed at τ_R ? 100 μ.     

EPR and IR spectra of Ni(ClO4)2)·6H2O between 98 and 298 K

EPR measurements between 98 and 298 K on single crystal of Ni(ClO₄)₂·6H₂O have indicated the appearance of a rhombic component in the axial crystal field at Ni²⁺ sites at T_c = 224 K, confirming a phase transition first reported by Chaudhuri from magnetic susceptibility measurements. Temperature variations of g, D and E parameters were determined. IR spectra at room and liquid nitrogen temperatures are consistent with our EPR results.     

The vibrational population inversion and relaxation kinetics of the C*2, d 3Πg state

The chemiluminescent spectra of C^*₂, d ³Π_g-a ³Π_u, Δ_v = O sequence from the reaction Na + CCl₄ have been obtained. The C^*₂, d ³Π_g,v' = 6 level is formed preferentially. The quenching and vibrational relaxation rates of the C^*₂, d ³Π_g state in Ar are 1.9 × 10⁶ and 2.2 × 10⁶ Torr^?1 s^?1, respectively. Na is one of the most efficient species for deactivation of C^*₂.     

The production of Cr(NH3)6 from the acid catalysed hydrolysis of Cr(NH3)5(NCO)

The rate of the reaction

has been investigated at 40–65°C with [HClO₄] varying from 0.04 to 0.6 M (μ = 0.6 M, NaClO₄). The observed rate law has the form: -d[Cr(NH₃)₅(NCO)²⁺]/dt = k_obs[Cr(NH₃)₅(NCO)²⁺] where k_obs = a[H+]²{1 + b[H⁺]²} and ^?1 at 55.0°C, a = 0.36 M^?1 s^?2 and b = 6.9 × 10^?3 M^?1 s^?1. The rate of loss of Cr(NH₃)₅(NCO)²⁺ increases with increasing acidity to a limiting value (at [H⁺] ～ 0.5 M) but the yield of Cr(NH₃)₆³⁺ decreases with increasing [H⁺] and increases with increasing temperature. In the kinetic studies the maximum yield of Cr(NH₃)₆³⁺ was 35% but a synthetic procedure has been developed to give a 60% yield.     

Conductibilité electrique aux basses températures des composés binaires Cr2X3 et Cr3X4 (X = S,Se ou Te)

Electrical resistivity of some binary compounds Cr₂X₃ and Cr₃X₄ (X = S, Se or Te) is studied on polycrystalline samples with the four point probe method, at temperatures between 4.2 and about 330 K. A metallic behavior is observed on Cr₂Te₃, Cr₃Te₄, Cr₃S₄ and the 3c′ form of Cr₂Se₃. Some other compounds are semiconductors: Cr₃Se₄ (E_300K ≈ 0.07 eV; E_4.2K = 2.07 × 10^?4 eV), the 2c′ form of Cr_2+εSe₃ (E_300K ≈ 0.074 eV; E_4.2K = 2.76 × 10^?4 eV) and the 3c′ form of Cr₂S₃ (E_275K ≈ 0.55 eV). The observed results seem to be closely related to the nature of the octahedral neighborhood of the cations.     

57Fe Mössbauer effect study of a presumed singlet-triplet transition in [Fe(P4)X]BPh4 complexes,X = Br,I

The ⁵⁷Fe Mössbauer effect in the solid compounds [Fe(P₄)X]BPh₄ (X = Br, I; P₄ = hexaphenyl-1,4,7,10-tetraphosphadecane) has been studied between 4.2 and 298 K. A single temperature dependent doublet is observed. For the iodo complex, ΔE_Q = 2.25 mm s^?1, δ^IS = +0.13 mm s^?1, V_tzz 0, η ≈ 0.8 at 4.2 K, whereas ΔE_Q = 1.81 mm s^?1, δ^IS = +0.20 mm s^?1 at 298 K. The results are consistent with a singlet-triplet transition with k > 10⁹ s^?1.     

Broken orbital symmetry study of low-lying excited and N15 ionized states of pyrazine

Ab initio ΔE_SCF calculations of the low-lying n-π^* and π-π^* transitions in pyrazines are reported with D_2h and C_2v symmetry adapted molecular orbitals. The use of broken orbital symmetry is essential for interpreting the emission properties of pyrazine at the computational level used. The energy of the N_is orbital is calculated using these two symmetry constraints with C_2v orbitals leading to results in better agreement with experiment.