The importance of spin relaxation in the delayed fluorescence of molecular crystals

Deactivation rate constants of spin-orbital excited Br atoms in the reactions Br(²P_{$\text{1}\text{2}$}) + O₂ → Br(²P_{$\text{3}\text{2}$}) + O₂ (k₁), and Br(²P_{$\text{1}\text{2}$}) + NO → Br(²P_{$\text{3}\text{2}$}) + NO (k₄) have been measured with a photodissociative IBr laser on the electronic transition ²P_{$\text{1}\text{2}$}?²P_{$\text{3}\text{2}$} in the Br atom (λ = 2.7 μm). The values obtained are (6.4 ± 1.8) × 10^?14 cm³ s^?1 and (1.9 ± 0.6) × 10^?12 cm³ s^?1, respectively. Comparison with published data leads to the conclusion that, contrary to a widely accepted point of view, the high rate constants for the quenching of excited halogen atoms are due to resonant energy transfer processes and not to the paramagnetic nature of the quencher.     

Synthesis and reactions of fluorinated iminium salts

Different methods for the preparation of fluorinated iminium salts RR¹CNR²R³⁺MF₆^? (R=R¹=F ; R²=R³=CH₃, C₂H₅ M=As, Sb 4a ? c R=H, R¹=F; R²=R³=CH₃ M=As, Sb 5a, b R=R¹=CF₃; R²=H, R³=CH₃ M=Sb 12 R=R¹=CF₃; R²=R³=CH₃ M=As 14) are reported, the spectroscopic properties (IR, NMR) of the cations of these salts are briefly discussed. By F^?-addition to these salts, $\text{e.g.}$ to 16, perfluoroalkyl-bis(alkyl)-amines ($\text{e.g.}$ (CF₃)₂CFN(CH₃)₂ 15) can be prepared; from the methylation of CF₃NCF₂ bis(trifluoromethyl) methylamine (CF₃)₂NCH₃ (11) was obtained.     

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 $\text{MW}\text{cm}{}^2$.     

A method for obtaining potential parameters for helium from T1 measurements

The temperature dependence of T₁ for ³He gas in the range 0–4°K is calculated for a Lennard-Jones (12,6) potential. The relaxation of the nuclear spins is assumed to be due to a dipolar interaction between the nuclei. A minimum value in the relaxation time, T_1,min, is found to occur at a temperature denoted by T_min. By repeating the calculation for different pairs of values of the potential parameters ? and σ, we have found that for a density of 10^?2 g/cm³,σ²T_min = 13.0?1.12 × 10³ ?σ², T_1,min/σ²(T_min)^{$\text{1}\text{2}$} = 17.4?6.56 × 10² ?σ², with ?, σ, T_min and T_1,min in eV, Å, °K and minutes, respectively. From measurements of T_min and T_1,min, ? and σ can be determined.     

Emission spectra of supersonically cooled methyldiacetylene cations

The ā²E → X?²E (Σ= + $\text{1}\text{2}$, - $\text{1}\text{2}$) electronic transitions of rotationally/vibrationally cooled CH₃CCCCH^- cation, as well as the d₁-/d₃-/d₄-substituted species, were studied by emission spectroscopy. Ion emission was obtained by electron impact on the neutral species seeded in a helium supersonic free jet. Vibrational frequencies in both electronic states are inferred to within ±1 cm^-1. Spin-orbit splittings are observed and interpreted on the basis of non-linear vibronic couplings. Rotational subbands are observed, yielding rotational and Coriolis parameters as well as rotational temperatures.     

An improved absorption correction based on a Gaussian ionization distribution model for electron probe microanalysis

The electron range equation R, employed in a Gaussian absorption correction, is optimized making use of f(χ) values which were calculated from ionization distributions determined experimentally by Brown and Parobek. A new expression of R[R = $\text{(1 + 2}\text{h}\text{)}\text{(1 +}\text{h}$)2.59 × 10^?5(E^1.3₀ ?E^1.3_c)] g cm^?2 is proposed in this paper.The absorption correction using the new electron range equation R is applied to oxygen determination in several silicates and sulfates with greater accuracy than other methods. This equation also predicts one of the most accurate mean depths of ionization at an accelerating voltage of 25 kV for Zn and Cd tracers in Al, Cu, Ag and Au matrices.     

Syntheses of σ-cyclobut-1-en-3-onyl complexes by cycloaddition of ketenes to some transition metal alkynyl complexes

Reactions of ketenes (R¹R²CCO) with (η⁵-C₅H₅)Ni(PPh₃)CCR (I) and (η⁵-C₅H₅)Fe(CO)(L)CCR (III, L = CO and PPh₃) give σ-cyclobut-1-en-3-onyl complexes, {(η⁵-C₅H₅)Ni(PPh₃)$\text{CC(R)COC}$}R¹R² (VI) and (η⁵-C₅H₅)Fe(CO)(L)$\text{CC(R)COC}$R¹R² (IX)}, (2 + 2) cycloaddition products, in good yields. The σ-cyclobutenonyl complexes also can be prepared by the reaction of I and III with acyl chlorides in the presence of triethylamine.     

Action of tert-butyl azidoformate on the conjugate bases of 1,2,3,4-tetrahydro-9H-carbazole and other indole derivatives

tert-Butyl azidoformate ($\text{2}$) reacts with the conjugate bases of $\text{3a}$, $\text{7a}$, $\text{9}$ (R¹ = R² = CH₃), and $\text{9}$ (R¹ = CH₃, R² = H) to give products [$\text{4}$, $\text{8}$, $\text{12}$, and $\text{14}$, respectively] in addition to the expected N-(tert-butoxycarbonyl)indole derivatives.     

Direct absorption measurement of the spin—orbit splitting of the ground state in atomic fluorine

We have measured the three hyperfine components of the spin—orbit split (²P_{$\text{3}\text{2}$} → ²P_{$\text{1}\text{2}$}) ground state in atomic fluorine by diode laser absorption spectroscopy. The measurement improves the accuracy of the two lines previously reported (404.175 and 403.969 cm^?1), with the third line at 404.210 cm^?1. This confirms the spacing of the hyperfine components measured by EPR, and establishes diode laser absorption as a viable technique for determining F-atom concentrations.     

Cleavage of iron2-alkenyl and iron2-alkynyl bonds by mercury(II) chloride

Reactions of HgCl₂ with η⁵-C₅H₅Fe(CO)₂R (R  CH₂CHCH₂ and CH₂C(CH₃)CH₂) in THF at 25°C rapidly afford $\text{1}\text{1}$ adducts of the two reactants. These adducts were converted to the corresponding PF₆^? salts, [η⁵-C₅H₅Fe(CO)₂(η²-CH₂C(R)CH₂HgCl)]⁺ PF₆^? (R  H and CH₃), for characterization. Slower reactions with cleavage of the ironcarbon σ bond and elimination of the R group from η⁵-C₅H₅Fe(CO)₂R occur for R  CH₂CHC(CH₃)₂, CH₂CHCHC₆H₅, and CH₂CCC₆H₅. Both elimination and $\text{1}\text{1}$ adduct formation are observed when R  CH₂CHCHCH₃. The kinetics of the cleavage reactions are presented and possible mechanisms for both cleavage and $\text{1}\text{1}$ adduct formation are discussed.     

A study of the near infrared emission bands of the hydroperoxyl radical at medium resolution

Emissions of the hydroperoxyl radical HO₂ in the spectral range from 1.0 to 1.6 μm were studied at low and medium resolution. The resolved spectrum shows the expected parallel band structure for the vibrational ovetone transition ²A″ (200-000); in the case of the vibronic transitions ²A′, 000 → ²A″, 000 and ²A′, 001 → ²A″, 000, however, comparison of experimental and computer simulated spectra shows that there also occur intense subbands with ΔK = 0, in addition to the ordinary ΔK = ± 1 transitions. The cause for the break-down of the type-C selection rule is not well known. In the reaction system of ethylene with discharged oxygen vibronic bands could be observed originating from ²A′ levels up to at least ν′₃ = 6. The most probable excitation mechanism for these high vibronic levels is the chemiluminescent reaction HCO + O₂ (¹Δ_g) → HO₂(²A′, 00ν′₂) + CO. From the computer fits to the spectra of HO₂ and DO₂ at medium resolution the origins of the 000-000 bands and the fundamental frequencies $\text{ν}$_3′ of the excited ²A′ state could be determined; the values are $\text{ν}$_o(HO₂)=7028 ± 3 cm^?1, $\text{ν}$_o(DO₂)=7034 ± 8 cm^?, $\text{ν}$_3′(HO₂)=927 ± 10 cm^?, and $\text{ν}$_3′(DO₂)=940 ± 28 cm^?1.     

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.     

Synthesis and molecular structure of niobocene(tricarbonyl)(π-cyclopentadienyl)molybdenum with metalmetal bond and unusual coordination of carbonyl groups

(C₅H₅)₂NbBH₄ reacts with C₅H₅M(CO)₃Me in toluene solution in the presence of Et₃N to give binuclear complexes (C₅H₅)₂NbM(CO)₃C₅H₅ where M is Mo or W (IV and V, respectively). The structure of IV has been studied by X-ray diffraction (the crystals are orthorhombic, a 12.748(5), b 16.745(6), c 14.314 $\text{A/ac>}\text{?}$;; Z = 8, space group of Pbca, automatic difractometer Syntex P2_I, λ(Mo-K_α, 1382 reflections, R = 0.056, R_w = 0.058). Molecule IV contains a wedge-like sandwich (π-C₅H₅)₂Nb (NbC 2.37–2.48, CC (av) 1.42 $\text{A/ac>}\text{?}$;, angle between ring planes 49°) linked with the (π-C₅H₅)Mo(CO) fragment by a direct NbMo bond (3.073 $\text{A/ac>}\text{?}$;) and two bridging CO groups, one nonsymmetrically bonded through the carbon atom only (CO 1.17, NbC 2.53, MoC 2.02 $\text{A/ac>}\text{?}$;) and the other σ-bonded to Mo (MoC 1.944 $\text{A/ac>}\text{?}$;) and π-bonded to Nb (CO 1.22, NbC 2.22, NbO 2.26 $\text{A/ac>}\text{?}$;). Three types of carbonyl groups present in IV give rise to strong IR bands at 1870, 1700 and 1560 cm^?1 assigned to the terminal, μ-bridging and σ, π-bridging CO groups respectively. Complex IV has a similar structure. The electronic structure of IV and its dissociation across the NbMo bond are discussed.     

Yield of I(2Psol:12) in the photodissociation of CH2I2

The production of I(²P_{$\text{1}\text{2}$}) in the photolysis of CH₂I₂ has been studied optoacoustically at excitation wavelengths between 365.5 and 247.5 nm. Bands found at 32200 and 47000 cm^?1 correlate with I(²P_{$\text{3}\text{2}$}) whilst those at 34700 and 40100 cm^?1, which correlate with I(²P_{$\text{1}\text{2}$}), give final ²P_{$\text{3}\text{2}$}/²P_{$\text{1}\text{2}$} ratios of 1.75 and 1.1, respectively, after curve crossing.     

Formation of an iridium σ-cyclopropane complex by the intramolecular activation of a cyclopropylphosphine: Rearrangement to a chelating σ-vinyl complex

When (t-Bu)₂PCH₂CHCH₂CH₂ is combined with [IrCl(C₈H₁₄)₂]₂ in toluene, the σ-bound cyclopropane complexes

(P(t-Bu)₂CH₂$\text{CHCH}{}_2\text{C}$H₂) (1a, 1b) are formed. Complexes 1a,1b react readily with H₂ to form IrClH₂P(t-Bu)₂CH₂$\text{CHCH}{}_2\text{C}$H₂)₂ (2). In polar solvents 1a,1b isomerize to the σ-vinyl chelated complex $\text{IrClH(P(t-Bu)}{}_2\text{CH}{}_2\text{C(CH}{}_3\text{)C}$H)(P(t-Bu)₂CH₂$\text{CHCH}{}_2\text{C}$H₂) (3). The structure of this 5-coordinate, 16-electron Ir^III complex was deduced from spectroscopic data, reaction chemistry, and from the crystal structure of its CO adduct (4). Compound 4 crystallizes in the monoclinic space group C_2h⁵-P2₁/n (a 15.610(14), b 15.763(16), c 11.973(13) Å, and β 104.74(5)°) with 4 molecules per unit cell. The final agreement indices for 2326 reflections having F_o² > 3σ(F_o²) are R(F) = 0.089 and R_w(F) = 0.095 (271 variables) while R(F²) is 0.148 for the 3423 unique data. Bond lengths in the 5-atom chelate ring $\text{IrPCCC}$ are IrP 2.341(4), PC 1.857(26), CC 1.520(30), CC 1.341(25), and CIr 1.994(21) Å. The IrCl distance is 2.479(5) Å.     

CH3O(X2E) production from 266 nm photolysis of methyl nitrite and reaction with NO

The CH₃O($\text{X}$²E) radical produced by the 266 nm photolysis of CH₃ONO is characterized by laser-induced fluorescence. Using a flowing gas cell the reaction rate of CH₃O($\text{X}$²E) with NO is measured to be (2.08 ± 0.12) × 10^?11 cm³ s^?1 molecule^?1 based upon disappearance of CH₃O and appearance of HNO detected by laser induced fluorescence. Upper limits for CH₃O reactions with CH₄, CO, N₂O, NH₃, CH₃OH, (CH₃)₃CH and CH₂CHCH₂CH₃ are reported. These reactions are all too slow to measure under our experimental conditions.     

The enthalpies of formation of CH3Mn(CO)5 and of CH3Re(CO)5, and the strengths of the CH3Mn and CH3Re bonds

From measurements of the heats of iodination of CH₃Mn(CO)₅ and CH₃Re(CO)₅ at elevated temperatures using the ‘drop’ microcalorimeter method, values were determined for the standard enthalpies of formation at 25° of the crystalline compounds: ΔH^o_f[CH₃Mn(CO)₅, c] = ?189.0 ± 2 kcal mol^?1 (?790.8 ± 8 kJ mol^?1), ΔH^o_f[Ch₃Re(CO)₅,c] = ?198.0 ± kcal mol^?1 (?828.4 ± 8 kJ mo^?1). In conjunction with available enthalpies of sublimation, and with literature values for the dissociation energies of MnMn and ReRe bonds in Mn₂(CO)₁₀ and Re₂(CO)₁₀, values are derived for the dissociation energies: D(CH₃Mn(CO)₅) = 27.9 ± 2.3 or 30.9 ± 2.3 kcal mol^?1 and D(CH₃Re(CO)₅) = 53.2 ± 2.5 kcal mol^?1. In general, irrespective of the value accepted for D(MM) in M₂(CO)₁₀, the present results require that, D(CH₃Mn) = $\text{1}\text{2}$D(MnMn) + 18.5 kcal mol^?1 and D(CH₃Re) = $\text{1}\text{2}$D(ReRe) + 30.8 kcal mol^?1.     

Synthesis of cationic dialkylgold(III) complexes: nature of the facile reductive elimination of alkane

A series of gold(III) cations of the type cis-[CH₃)₂AuL₂]⁺ X^? where L  Ph₃, PMePh₂, PMe₂Ph, PMe₃, AsPh₃, AsPh₃, SbPh₃, $\text{1}\text{2}$H₂NCH₂CH₂NH₂, $\text{1}\text{2}$ Ph₂PCH₂CH₂-PPh₂, $\text{1}\text{2}$ Ph₂AsCH₂CH₂AsPh₂, and $\text{1}\text{2}$o-C₆H₄(AsMe₂)₂ and X  BF₄^?, PF₆^?, ClO₄^?, and F₃CSO₃^? has been prepared. In addition, the cis complexes [(CH₃)(CD₃)-Au(PPh₃)₂]F₃CSO₃, [(C₂H₅)₂Au(PPh₃)₂]F₃CSO and [(n-C₄H₉)₂Au(PPh₃)₂]F₃-CSO₃ have been synthesized. All have been characterized by PMR, Raman and infrared spectroscopy. These [R₂AuL₂]X compounds yield only ethane, butane, or octane via reductive elimination, and no disproportionation is observed. The alkane eliminations have been studied in CHCl₃, CH₃Cl₂, and CH₃COCH₃ solution as a function of temperature, concentration of the complex, and concentration of added ligand L. Elimination is fastest when L is bulky (PPh₃ > PMePh₂ > PMe₂Ph > PMe₃), decreases in the sequence SbPh₃ > AsPh₃ > PPh₃, is slow with chelating ligands, is inhibited by excess ligand, and there is small anion effect as X is varied. As R is varied, the rate of elimination decreases Bu ? Et > Me. An intramolecular dissociative mechanism is proposed which involves rapid elimination of alkane from an electron deficient dialkylgold(III) complex with nonequivalent gold—carbon bonds and produces the corresponding [AuL₂]X complex.     

Energy levels of iodine monochloride near the first dissociation limit

Absorption transitions to vibrational levels close to the A state dissociation limit of ICI have been examined using a two-photon sequential absorption technique. The discrete rotational structures of I³⁷ Cl bands to within 0.7 cm^?1 of the limit have been selectively excited and analysed. A value of 17557.514 ± 0.030 cm^?1 has been obtained for the I(²P^o_{$\text{3}\text{2}$}) + Cl(²P^o_{$\text{3}\text{2}$}) dissociation energy D_e, relative to the minimum of the ICI ground state potential well. The two-photon technique can be used to excite and display separately the high resolution absorption spectra of different isotopic species of a molecule which are contained in a mixture.     

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.