The earliest studies concerned photoelectric emission of negative charges from dyestuff solutions,1,2 and anthracene layers.3 The negative charges were identified as electrons,4 then in 1911 Goldmann and Kalandyk5 separated photoconduction from photoelectric emission, observing it in anthracene under U.V. irradiation, while Pauli6 and Volmer7 studied photoconduction in anthracene in the visible. Petrikaln8 discussed gas effects on visible light photoconduction in dyestuffs, Koenigsberg and Schilling9 studied dark conduction in anthracene, naphthalene and alizarine and also deduced the formula linking specific conductivity a with absolute temperature T, [sgrave] = [sgrave]0,exp(-Eact/kT). Further dark conduction studies were carried out by Rabinowitsch.

The time dependence of pulsed photoconduction in two tetracyanoquinodimethane (TCNQ) complex salts, 1,4-di-(N-pyridinium) butane (TCNQ)4 and 2,3-bis(1-methyl-4-pyridium) butane (TCNQ)4, was investigated. Each sample exhibited, at the same temperature, structureless dispersive (non-Gaussian) current transients, characteristic of a highly disordered solid. Similarities with doped disordered polymer systems were found. Shallow-trap modulated hole mobilities of order 10−3 to 10−4 cm2 V−1 s−1 were deduced. However, above 170 K the current transients in samples of one salt showed structure in the microsecond range, suggesting a hole mobility within the valence band of approximately 8 cm2 V−1 s−1.

Emulsions of simulated sea water in crude oils or in model oils containing dispersed asphaltenes have been studied using a Couette viscometer. Non-Newtonian behavior was observed for the model oil emulsions and for some of the crude oil emulsions with high water contents and small droplet diameters.

Surface tension measurements have been made on aqueous solutions of poly(methyl vinyl ether) containing electrolytes. The surface tension of polymer solutions fell linearly with increasing concentration of NH4Br, LiCl, NaNO3, Ca(NO3)2 Al(NO3)3, NaF, CsF and KF. With the exception of calcium and aluminium nitrates, the rate of decrease in the surface tension correlated with the electrostriction properties of the salts. The results are discussed in terms of the McDevit–Long theory.

The compressibilities of crude oil/water interfaces have been measured for Brega, Kuwait and Tia Juana crude oils by an adaptation of the pendant drop method. Addition to the oils of a commercial dispersant (BP1100X) which contains an oil-soluble non-ionic surfactant resulted in increased compressibilities, the rate of increase with amount of BP1100X added being inversely related to the asphaltene content of the oils.

AbstractKinetics and mechanism of heterogeneous catalytic N2O decomposition has been studied on Pd single‐crystal surfaces and polycrystalline wires (830‐ 1000 K, 0.05‐ 1.0 Torr).

Davy's hot-wire method has been developed for PdAu wires and H2 in air, to find the relation between alloy composition and ignition temperature. The activation energy for the surface ignition reaction has been derived, on certain assumptions, and its relation to PdAu composition found to parallel that for the para-H2 conversion and H2+ D2 reactions. It has therefore been suggested that H2 activation is the critical step for surface ignition on the PdAu surface, expressible in general terms as Oad+H2→ H2O +□ where □ denotes on empty site on the wire surface.

The following topics, taken from the three preceding surface science papers, are discussed in the light of conventional kinetics: subsurface adsorbed O 2- , molecular beam results for H 2 + D 2 on Cu, Pt and Pd, ethylene hydrogenation, S-adsorbate interactions, and the evolution of ‘catalytic entities’. Work with single-crystal planes eliminates multiple-plane and grain-boundary effects found in wires and evaporated films, but still leaves, in many cases, complications due to lateral interactions in adsorbates. Also, in our experience, single-crystal planes yield m ore accurate and reproducible data than polycrystalline specimens.

The catalysed decomposition of N2O in the range 830–1000 K and 0.05–1.0 Torr (1 Torr ≈ 133 Pa) has been examined on Pd single-crystal surfaces and polycrystalline wires and compared with earlier work. The relative reaction velocities at 1000 K and 0.2 Torr are as follows: 0.01 cm diameter wire, 21; 0.025 cm diameter wire, 10.9; (610) plane, 2.2; (100) plane (thin disc), 1.8; (110) plane, 1.8; (100) plane (normal thickness disc), 1.7; and (111) plane, 1.0. Kinetic equations describing the first-order inhibition in oxygen pressure derived earlier by Eley and Knights for O2 chemisorbed as molecules have been rederived in terms of an adsorption–desorption reaction between chemisorbed oxygen atoms and 'transitional' or 'subsurface' oxygen atoms. The apparent activation energies for Pd (and for the earlier PdAu wires) have been discussed in terms of this mechanism. From the above, 'stepsites' on (610) furnish sites ca. 2.7 times more active than terrace sites on (100), while grain boundaries may well be responsible for the more active sites on the Pd wires. By implication, since pure Au is known to show negligible chemisorption of O2 at 1000 K, it seems possible that grain boundaries furnish the only active sites for N2O decomposition on that metal.

Hydrogen absorption to give the dihydrides MH 2+1 containing interstitial hydrogen H i has been studied for the metals Gd, Dy, Er, Yb and Lu in the form of films deposited in ultra-high vacuum on glass. Film areas were determined by Kr adsorption, and hydrogen content, in particular inter­stitial hydrogen H i , characterized by gas uptake, temperature programmed desorption, electrical conductivity and work function measurements by the diode method. The catalytic activity of the dihydride films for the H 2 + D 2 → 2HD reaction was studied at a pressure of 1.1 Torr over 175-579 K, and at 273 K over 0.19-6.2 Torr. Arrhenius plots for the rate con­stant show a low temperature low activation energy region changing over at a temperature T c to a higher temperature higher activation energy régime, with T c on average for the five metals about 50 K below the tem­perature T max at which the interstitial hydrogen H i has disappeared. The suggested mechanisms are T < T c : D 2 + H i □ s → (D 2 H i )□ s → □ s D i + HD, (1) T > T c : D 2 + H 2 + 4□ s → 2(D i □ s ) (H i □ s ) → 4□ s + 2HD, (2) where H i □ s , D i □ s , denotes a hydrogen, deuterium, atom held on a surface octahedral site in the f. c. c. metal sublattice. These mechanisms agree with the observed approximate first-order pressure dependency down to 77 K. The rate constants at both 273 K (under T c ) and 573 K (over T c ) decrease over Gd, Dy, Er, to Yb, and rise again to Lu, and this is discussed in terms of the metal-hydrogen, H i □ s or D i □ s bond strength.

AC conductivity in the range 10 to 105 Hz of N, N′-diethyl- and N, N′-dibenzyl-4,4′-bipyridylium (TCNQ)4 consists of a frequency independent part, identified with dc conductivity, and a frequency dependent part resulting from hopping of carriers between localised sites. The density of hopping carriers is a sensitive indicator of the degree of perfection of the crystal and is significantly increased by grinding and compression. AC conductivité dans l'échelle 10 à 105 Hz de N,N'-diethyl- et N,N'-dibenzyl-4,4'-bipyridylium (TCNQ)4 est composée d'une partie qui est indépendante de la fréquence, identifiée avec conductivité dc, et une partie qui est dépendante de la fréquence occasionée par le saut de porteurs entre des emplacements localisés. La densité de porteurs sautants est un indicateur qui est sensible au degré de perfection du cristal et qui est augmentée considérablement á force de broyer et de comprimer.

Bimodal cavities were found to give a Faraday rotation in a magnetic field, arising from the Hall effect in the cavity walls, which seriously limited the application of this technique to low-mobility materials. Methods of reducing the empty cavity signals are described, and new results are reported for biological materials which differ from earlier published values. In particular, no support can be adduced for earlier views on band conduction in the mitochondrial electron transfer system.

Surface isotherms have been determined over the temperature range 277–291 K for poly(vinyl methyl ether) films spread on water and on dilute salt solutions in a Langmuir–Adam surface balance. The results are interpreted in terms of an electrostriction effect in the surface region. Parameters derived from the fitting of theoretical equations of state are related to the electrostriction partial molal volumes of the salts by application of the McDevit–Long theory.

A new cell is described which permits the measurement of both electrical conductivity and the Seebeck coefficient along any particular axes of the small, fragile, anisotropic single crystals of TCNQ complex salts and related compounds.

The steady-state temperature distribution has been determined along a 9 cm 32 SWG Pd wire axially stretched in a reaction vessel and electrically heated in vacuo and in 26 Pa oxygen. The results have been used to calculate reaction velocity for the model rate km=Bm exp (–E/RT), with Bm= 1025 molecule m–2 s–1, and with E= 80–180 kJ mol–1. 'Experimental'E′ and B″ values were then calculated using the maximum (central) wire temperatures T′ and E″ and B″ values using the computed average wire temperatures T″. For the range of E, the E′ and B′ values correspond more closely for the gaseous ambient to the true (E and 1025) values. If we assume a simple linear extrapolation to lower E values than 80 kJ mol–1, then below E= 30 kJ mol–1, E″ will correspond more closely to the true E values. The generalisation of these conclusions is discussed in relation to some earlier studies on catalytic wires.

Abstract The observed anisotropy reflects a 2D array of TCNQ's. A plateau in the logo vs T−1 plots is computer fitted to the Roberts-Schmidlin model of states in the band-gap, with electrons as majority carriers. The predicted Seebeck coefficient is correct in sign (negative) and temperature-dependence, but too large, suggesting a hole contribution to the carriers; structural disorder is clearly a factor.

Temperature programmed desorption (TPD) of CO and O2 on PdAu alloy wires has been studied. The heat of adsorption, sticking coefficient and maximum coverage of CO were recorded for Pd, 83 Pd 17 Au, 60 Pd 40 Au. For Pd and Pd-rich alloys the heat of adsorption remained fairly constant but the maximum coverage fell markedly from 0.42 for Pd to less than 0.05 for bulk palladium atom fraction XBpd ⩽ 0.83. The heat of adsorption, sticking coefficient and maximum coverage of O2 were investigated for pure Pd. A very limited adsorption was recorded on 83 Pd 17 Au and none on the more Au-rich alloys. The adsorption data are used to discuss the CO + O2 reaction. Activation energy and frequency factor are estimated on Pd, for the TPD conditions used here. Earlier rate constants (0.2 Torr, 150°C) for CO + O2 on PdAu as a function of Au content correlates with the maximum coverage of chemisorbed CO, which in turn is correlated with the probability of finding a Pd9±1 ensemble in the surface. Modern results on the d-band structure of the PdAu alloys suggest that the Pd9 ensemble, i.e. a surface Pd atom without an Au atom in its coordination shell, would tend to optimise both the donor and acceptor actions of the Pd atoms involved in chemisorbing CO.

AbstractPhotocurrents in single crystals and compressed discs of methyltriphenylphosphonium (TCNQ)2− can be observed at low temperatures where the dark current is greatly reduced, or by the use of a chopped light source and a narrow band amplifier or oscilloscope display. By chopping at appropriate frequencies the true photocurrent can be observed and bolometric effects eliminated. The true photocurrent, which is ohmic and linear with light intensity, shows a threshold at (2.7 ± 0.1) μm. The carrier lifetime is 140 ms above and below the phase change at 310 K, but at the phase change more than one lifetime is observed due to trapping.