R.F.C. Claridge

Fluorescence of aliphatic amines

Abstract Fluorescence of several tertiary aliphatic amines has been excited in the gas phase by absorption of 206.2 nm radiation, i.e. in the band corresponding to the A - X transition of NH3. No fluorescence was obtained from molecules having hydrogen or deuterium bonded directly to the nitrogen atom. The experiments support the view that quantum-mechanical tunnelling is the major factor governing the rates of predissociation of the excited states of NH3, ND3, and simple amines.

Radiative lifetime of the NH3 - Hg(3P0) complex

Abstract A lifetime of (1.86 ± 0.08) × 10 −6 sec has been determined from phase-shift measurements of the luminescence emitted when the NH 3 ·Hg( 3 P 0 ) complex dissociates. The lifetime is independent of the ammonia pressure. By allowing for the finite lifetime of the complex improved values of the rate constants for reaction of NH 3 with Hg( 3 P 0 ) have been obtained.

Band fluorescence of xenon

The Xe2 emission band at 168 nm has been observed during irradiation of xenon gas with the 147 nm resonance line. The band is attributed to Xe2 molecules formed by reaction between ground-state and metastable (2u) xenon atoms.

The reaction of NH3 with Hg(3P0)

A modification of the rotating sector method has been used to study the mercury-photosensitized luminescence of ammonia. At low ammonia pressures the intensity of the modulated luminescence decreases rapidly with increasing frequency of modulation, showing that a slow process must intervene between the rapid quenching of Hg(3P1) by NH3 and the rapid emission of radiation by the excited HgNH3 complex. It is postulated that the initial quenching step results in the formation of metastable Hg(3P0) and that the slow process is the reaction of this species with NH3. From the variation of emission intensity with modulation frequency the rate of the slow step is found to be 4.3 × 10−13 cm3molecule−1sec−1.

Interactions in crystals LXXVIII. The structure of “naked” 9,10-bis(trimethylsilyl) anthracene radical anion☆

Abstract Reduction of 9,10-bis(trimethylsilyl)anthracene at a sodium metal mirror under aprotic conditions and argon yields its radical anion, which is characterized by its ESR multiplet signal pattern. Crystallization from dimethoxyethane solution under aprotic conditions yields brown prisms of its solvent-separated radical anion salt. The structure, determined in a 130 K cold N 2 flow, is discussed in comparison with the analogously folded structure of the neutral molecule, literature examples and results of MNDO calculations.

Excimer formation by NH3 and Cd(3P0

Abstract A weak emission band between 380 and 500 nm has been observed during irradiation of a mixture of NH 3 and Cd vapour with Cd 326.1 nm radiation. The kinetics of the reactions leading to light emission have been studied by a phase-shift method. The rate constant for the reaction Cd( 3 P 0 ) + NH 3 → products is (1.7 ± 0.3) × 10 −12 cm 3 molecule −1 sec −1 at 560°K. The mean lifetime of the Cd.NH* 3 complex is (4.9 ± 0.2) × 10 −7 sec.

Phase-shift study of the quenching and trapping of Cd 228.8 nm resonance radiation

Abstract Cadmium vapour at ∼ 560 K has been irradiated with 228.8 nm radiation from a microwave discharge lamp modulated at 30 kHz. The phase angle of 228.8 nm fluorescence, relative to a fixed reference signal, has been measured as a function of the partial pressure of quenching gas. Rate constants k Q for the quenching of Cd (5 1 P 1 ) have been calculated from: where T is the trapping time for resonance radiation in the presence of N Q molecules of quencher per cm 3 , and T 0 is the trapping time in absence of quencher. Trapping times were determined from the phase shift between the exciting light and the fluorescence; the phase angle corresponding to zero phase shift was obtained by an extrapolation procedure. Values for k Q are given for Q = He, Ar, H 2 , N 2 , NH 3 , N 2 O, CO 2 , CO, propene and n-butane. The values range from 5.2 × 10 −12 to 1.5 × 10 −9 cm 3 molecule −1 s −1 ; T 0 was typically 1.4 μs.

Dissociation energy of the NH3 · Hg(3P0) complex

Abstract A phase-shift method has been used to study the bimolecular and termolecular reactions of Hg(3P0) with NH3. The bimolecular and termolecular rate constants are 3.8 × 10−13 cm3 molecule−1sec−1 and 1.4 × 10−30 cm6 molecule−2sec−1, respectively. From the difference between the wavelengths of peak emission intensity for the stabilized and unstabilized Hg·NH3 complexes the dissociation energy of the complex is estimated to be 5.0 kcal mole−1.

The reactions of xenon and mercury with Hg(3P0)

Abstract The emission band arising from a charge-transfer complex of Xe and Hg(3P0) has been observed during 253.7 nm irradiation of mixtures of mercury and xenon, both with and without the addition of nitrogen to promote the formation of metastable mercury atoms. Helium, neon, argon and krypton gave no comparable luminescence but merely broadened the Hg 253.7 nm line. The rate constant for reaction of Xe with Hg(3P0), as determined by a rotating sector method, is (3.8 ± 0.4) × 10−15 cm3 molecule−1 sec−1. From the variation of the measured rate with the mercury vapour pressure the rate constant for reaction of ground-state Hg with Hg(3P0) was found to be (1.9 ± 0.5) × 10−11 cm3 molecule−1 sec−1.

Studies of the temperature dependence of the EPR spectra of some peri-alkylnaphthalene anions

Abstract Linewidth alternation effects are reported in the EPR spectra of the radical anions of some nonplanar peri-alkylnaphthalene compounds over a range of temperatures. These are analysed using a modified-Bloch-equation approach in terms of the movement of the aliphatic substituents. Estimates of the activation energies for this movement are made and these compare favorably with the value observed for chair-boat interconversion in the cyclohexane molecule.