A variational calculation of the lower-lying vibrational energy levels of the ammonia molecule is performed, in which all six vibrational degrees of freedom are treated simultaneously. A literature potential is assumed for all non-inversion motions; a new inversion barrier potential with a barrier of 1616 cm

A new variational calculation of the inversion spectrum of ammonia is reported in which all six vibrational degrees of ammonia are employed. By fitting spectroscopic data, an inversion barrier of 1810 cm"1 is obtained.

Significant structure theory leads to a partition function which accounts for all three phases of simple substances and in particular describes rather accurately the liquid and dense gas regions.' In the case of polyatomic molecules, additional degrees of freedom not possessed by monatomic molecules must be taken into account, and for light molecules like hydrogen, quantum effects must be considered.2 We present here a modification of the basic partition function to account for hindered intermolecular rotation.The Significant Structure Model (refs. 1 and 2).-The problem of describing a condensed system is really the problem of determining the distribution of the normal modes of motion of the molecules. This distribution follows from our liquid model, according to which all the molecules vibrate much as in a solid except for molecules jumping into vacancies. The result is that a vacancy surrounded by molecules converts three vibrational degrees into translations, and in so doing the vacancy behaves as a gas molecule. Since vacancies are of molecular size, the number of moles of vacancies in a mole of liquid is V -V,/VS, where V is the molar volume of the liquid and V, is the molar volume of the solid at the melting point. A vacancy surrounded by other vacancies is without dynamic properties, but when it is completely surrounded by other molecules, it acts like a gas molecule. Since the fraction of the positions next to a vacancy filled by molecules is V8/V, we write (V8/V). (V -V./V.) = (V -V8/V) for the fraction of gaslike molecules, with the remaining fraction VS/V being solidlike. Accordingly, for simple molecules like liquid argon, our model leads to the partition functionwhere the numerical value of all parameters is calculated from the model. This formula should apply equally well for polyatomic molecules if proper account is taken of hindered rotation and of the internal vibrations. The internal vibrations are practically unchanged by any phase change so that they offer no difficulty.A Simplified Partition Function for Hindered Rotation.-Some solids show higherorder transitions below the melting point which have been interpreted to be due to the onset of molecular rotation.3 Some members of series of similar compounds do not show any transitions below the melting point but do have large entropies of

Sons, Somerset. 1978, v This volume contains papers submitted to a symposium in celebration of the 500th anniversary of the University of Uppsala. or^ ganized by the Uppsala Quantum Chemistry Group and published as a supplement to volume XI1 of the International Journal of Quantum Chemistry, the symposium attracted not only quantum chemists and specialists in neighboring fields such as astronomy, molecular spectroscopy, solid state and surface physics, and quantum biology, but also a number of scientific philosophers to place the relatively infant field of quantum chemisty so valuable in our century, in perspective appropriate to the occasion.T h e thirty-four contributions to this volume leave one with the impression of a quantum chemistry symposium on a grand scale reviewing the many advances made in diverse areas in recent years, yet keeping an eye toward the future. The subject matter is roughly dichotomized into presentations of the rather specialized current applications and methods one would expect to see at a world symposium of quantum chemists, and mare introspective and speculative accounts of trends in quantum chemistry. Particularly noteworthy to teachers are the very clear a e~ counts of interpretation in quantum theory by Bunge, KBlnay, Kanstad, Layzer, Linderberg, Woolley, and Levy-Leblond, culminating in Lawdin's well-organized comprehensive (albeit preliminary) unification of quantum and classical mechanics and thermodynamics, based on the mathematics of a trace algebra.Qualitative discussions of the predictive power of wave mechanics applied to chemical reactions by Ohno (nonempirical calculations), Fukui (reactive orbitals), Halevi and Schrieffer (potential-energy surfaces) as well as articles dealing with applications to hiological problems by Demoulin et al. (bioinorganic chemistry), MeLachlan (protein folding), Sung and Szent-Gy6rgyi (cancer theorv) will also beof interest to nonsoeciulistr. I'hc remainill: III~ r g twhnwal p.rlrer, will be berkrapprvci2,~wl l~y..pe, ~1 1 . t~ i n tne various areas.

in the 810 pages of the volume.The book is not intended as a text and would not be suitable for that purpose. I t does, however, provide an up-to-date (1976) survey of a variety of aspects of solid-state reactivity. Mast of the experimental methods currently used in investigations of solids are illustrated in one or more of the contrihutions. Overall, the book presents a good picture of the "state-of-the-art" and cites a number of areas where further investigation is needed. It is especially appropriate as a reference volume for libraries of institutions and individuals involved in solid-state res e m h .