Akira Inaba

Calorimetric study of proton tunneling in solid 5-bromo-9- hydroxyphenalenone and deuteration-induced phase transitions in its deuteroxy analog

The heat capacities of 5-bromo-9-hydroxyphenalenone (BHP) and its deuteroxy derivative (BDP) were measured at temperatures between 2 and 310 K. The heat capacity of BHP is a smooth function of temperature and that of BDP has two peaks at 21.3 and 33.9 K. By analyzing the data on BHP, a tunnel splitting of (64±2) cm−1 associated with the quantum mechanical motion of the hydrogen atom in the intramolecular O–H–O hydrogen bond was derived along with the Debye temperature 60.8 K and two Einstein temperatures 131.4 (nondegenerate) and 210.4 K (doubly degenerate). The enthalpy change of 225 J mol−1 and entropy change of 6.8 J K−1 mol−1 were determined for the total thermal effects associated with the two phase transitions in BDP. The value of the transition entropy is consistent with the twofold disorder in the high temperature phase. The tunneling energy and transition enthalpy satisfy an inequality demanded, on the assumption that the potential energies experienced by the proton and deuteron are the same, by ...

Proton tunnelling and deuteration-induced phase transitions in hydrogen-bonded crystals

Experimental facts about appearance of new crystalline phases at low temperature related to deuterium substitution are collected and mechanisms of the isotope effect discussed. Compounds considered are (i) tri-alkali hydrogen selenates and sulphates, (ii) ammonium hexachlorometallates, (iii) bromo- and iodo-hydroxyphenalenone and (iv) chromium hydrogen dioxide. In (i), (iii) and (iv), linear O-H-O hydrogen bonds are involved. Proton tunnelling is the likely mechanism of the peculiar phase behaviour of (i). Definitely the tunnelling plays an essential role in (iii) but not in the extreme situation in (iv). In (ii), rotational tunnelling of an ammonium ion is the likely ingredient of the deuteration-induced phase transitions. The term proton cloud is introduced to describe the quantum mechanical distribution of the nucleus in the hydrogen bond and in the multi-valley rotational potential for an ammonium ion.

Calorimetric Investigation of the Monolayers Formed At Solid-liquid Interface

Heat capacity measurements have been made to investigate the formation of two solid monolayers each of n-pentane, n-heptane and n-dodecane adsorbed on graphite, one at submonolayer coverages and the other coexisting with the liquid. At submonolayer coverages the monolayers are found to melt respectively at 99.8, 151.6, and 217.3 K, well below the bulk melting points. The monolayers coexisting with the liquid melted at 205.6 for heptane and at 287.8 K for dodecane, whereas no evidence was obtained for pentane on the formation of such solid monolayer above the bulk melting point. The order persisting in the liquid near the interface depends upon the length of the molecules. The dodecane monolayers showed another transitions below the melting points both at submonolayer and multilayer coverages.

The investigation of mixed monolayers adsorbed from solution: octane and nonane mixtures on graphite

The combination of sensitive calorimetry, incoherent elastic neutron scattering and neutron diffraction has been used to demonstrate the formation of solid layers containing both octane and nonane adsorbed onto graphite from the binary alkane mixture. This combination of methods allow us to characterise the adsorbed layer in some detail including the absolute composition and melting temperature as a function of solution composition. The evidence presented here suggests that the two alkanes exist on the surface as patches of pure material not as a single crystal incorporating both alkanes.

NEW SCATTERING TECHNIQUES TO CHARACTERISE THE STRUCTURE OF SOLID MONOLAYERS ADSORBED FROM CONDENSED PHASES TO SOLID SUBSTRATES

Abstract Incoherent elastic neutron scattering is demonstrated to be a powerful technique for the investigation of molecular layers adsorbed at buried solid/liquid interfaces. Examples of the system exhibiting the formation of solid monolayers include alkanes, alcohols and organic acids adsorbed from their liquids and organic acids adsorbed from alkane solution. The behaviour of these systems is in marked contrast to that of a simple liquid crystalline molecule which does not show any evidence of forming a solid adsorbed monolayer.