Showing papers in "Annual Review of Physical Chemistry in 1969"

Theories of Liquids

Abstract: Since Henderson's review ( 1) of liquids appeared in the Annual Review of Physical Chemistry in 1964 , there have been many books and review articles written about liquids , and one of the tasks in writing yet another review at this time is to decide which topics have been sufficiently reviewed already. Among the topics which might have been considered for review here are computer studies of liquids , equations of state, critical phenomena, the melting transition, solutions , transport phenomena, quantum liquids , surface tension, water , distribution function theory , liquid m etals , and inelastic and elastic scattering in liquids. For a variety of reasons , including a limitation of space, we have chosen to review only the first four of these topics , although very special aspects of some of the other subjects do appear under other headings. We would like to point out that all of these last topics have been reviewed recently, and indeed solutions (2) are reviewed in another article in this volume. Among the many articles which have appeared in the last 4 or 5 years on transport phenomena are recent reviews by Rice, Boon & Davis (3) and by Nicolis and associates (4). Quantum liquids are currently receiving much attention and are discussed , for example, in books by Pines & Nozieres (5) and by Brewer (6). Studies of surface tension have been reviewed by Buff & Lovett (7). Recent reviews on water are contained in the book , The Structure and Properties of Water by Eisenberg & Kauzmann (8) and in an article by Conway (9). Discussions of recent developments in distribution function theory, including the improved Percus-Y evick (PYII) and improved hy­ pernetted-chain ( HNCII) integral equations ( 10) are to be found in an article by Rushbrooke ( 1 1) and in a book by Cole ( 12). Although we shall not review this topic , we wish to m ention that one problem which is currently of interest is that of obtaining the intermolecular pair potential from the experim entally d etermined radial distribution function by way of the distribution function theory of liquids ( 13 , 14). R ecent reviews of liquid m etals include the book Liquid Metals by March (15) and the conference proceedings , The Properties of Liquid Metals, edited by Adams, Davis & Epstein ( 16). Finally , in our list of reviews of topics not covered here are the reviews of inelastic and elastic scattering from liquids. The development of the laser has resulted in greatly improved techniques ( 17-19) for studies of light scattering , and these new techniques will un-

Electronic Spectroscopy by Electron Spectroscopy

Abstract: Confronted with the stupefying flow of new information in the field of electronic spectroscopy, we have selected for review here three closely related topics likely to be less familiar to many of the readers of A nnual Reviews of Physical Chemistry than conventional spectroscopic methods. We do this in order to direct attention to a group of methods j ust now becoming especially fruitful for the study of electronic states of molecules. The methods are electron impact spectroscopy, photoelectron spectros­ copy, and Penning ionization spectroscopy. They have in common one facet that distinguishes them from conventional spectroscopy : all three of these methods use energy analysis of electrons, rather than energy analysis of photons, as the primary source of information. The three methods differ both in the manner by which excitation is induced, and in the kind of informa­ tion one obtains. I mpact spectroscopy obviously relies on transfer of kinetic energy from a free electron to the bound electrons of a target molecule or, as we shall often refer to it, a scatterer. This method is useful for studying normally empty levels, and particularly for studying transitions normally "forbidden" in conventional optical spectroscopy. Photoelectron spectros­ copy uses monoenergetic photons to remove bound electrons from targets and is particularly useful for studying normally occupied levels, including levels from the valence shells all the way to the most tightly bound K-shells. Penning spectroscopy is a new field, in which excitation is delivered to the target in the form of a quantum bound to an incoming atom, i.e., an excited, often metastable species. The Penning ionization process has the form A*+ M-7A+ M+ + e. This method is proving useful for the study of normally filled levels, particularly in the valence shell. Several reviews of topics related to electron spectroscopy should be noted. In connection with electron impact spectroscopy, the subject of forbidden transitions, the theory of excitation and ionization by electron impact and the measurement of these processes were reviewed in 1962 by Garstang (1) , Seaton (2) , and Fite (3) , respectively. Peterkop & Veldre have reviewed the theory of electron-atom collisions (4). Electron impact ionization cross sec­ tion data was surveyed by Kieffer & Dunn (5) , and Moiseiwitsch & Smith have reviewed electron impact excitation of atoms (6) . A review by Bardsley & Mandl of resonant electron-atom and electron-molecule collisions has