Adsorption quantum effects

In Sec. II we briefly review the experimental situation in surface adsorption phenomena with particular emphasis on quantum effects. In Section III models for the computation of interaction potentials and examples are considered. In Section IV we summarize the basic formulae for path integral Monte Carlo and finite size scahng for critical phenomena. In Section V we consider in detail examples for phase transitions and quantum effects in adsorbed layers. In Section VI we summarize. 

In this review we consider several systems in detail, ranging from idealized models for adsorbates with purely repulsive interactions to the adsorption of spherical particles (noble gases) and/or (nearly) ellipsoidal molecules (N2, CO). Of particular interest are the stable phases in monolayers and the phase transitions between these phases when the coverage and temperature in the system are varied. Most of the phase transitions in these systems occur at fairly low temperatures, and for many aspects of the behavior quantum effects need to be considered. For several other theoretical studies of adsorbed layer phenomena see Refs. 59-89. 

H. Tanaka, H. Kanoh, M. El-Merraoui, W.A. Steele, M. Yudasaka, S. Ijiima, K. Kaneko, Quantum effects on hydrogen adsorption in internal nanospaces of single-wall carbon nanohorns. J. Chem. Phys. B, 108(45) (2004) 17457-17465. 

Because of its small size (collision diameter 0.20 nm), helium would appear to be a useful probe molecule for the study of uitramicroporous carbons. The experimental difficulty of working at liquid helium temperature (4.2 K) is the main reason why helium has not been widely used for the characterization of porous adsorbents. In addition, since helium has some unusual physical properties, it is to be expected that its adsorptive behaviour will be abnormal and dependent on quantum effects. 

Characterization of nanopores must be carried out with integrated information from different levels and angles. It is shown that gas adsorption can provide a key information in the integrated characterization of nanopores. In particular, further understanding of pore filling is necessary an evidence on quantum effect in pore filling and a new method of adsorption isotherm from P/Po = lO" are introduced with the relevance to the nanopore characterization. 

Kaneko et al attempted to apply He adsorption at 4.2 K for evaluation of ultramicropores in activated carbon. [34] Although He adsorption at 4.2 K is efficient for detection of presence of ultramicropores, quantitative evaluation of ultramicroporosity is still difficult a kind of quantum effect is speculated. Johnson et al pointed that quantum effect is predominant in hydrogen adsorption in SWNT from their theoretical studies. [35] We need a small probe molecule for ultramicropore characterization. At the same time, contribution by quantum effect must be understood in order to establish nanopore characterization using the small probe molecule. 

Tanaka et al measured Ne adsorption on well-crystalline AIPO4-5 at 27 K to 33 K near boiling temperature of Ne and calculated the DFT isotherm, suggesting the presence of quantum effect.[36] Thus, even Ne molecules show quantum effect. Small probe molecules such as He and H2 should show a pronounced quantum effect. 

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