molecular species and permit the study of state-to- 

 state selective chemistry. Thus, detailed dynamics 

 of state-to-state bimolecular collision processes 

 can he determined. These experimental studies are 

 complemented by theoretical work on molecular 

 excited states. Experimental investigations have 

 indicated the inadequacy of the conventional rate 

 theory model (based on the activated complex) for 

 predicting vibrational enhancement of chemical 

 rate processes in certain systems. This activated 

 complex model has been a central fixture in chemi- 

 cal kinetics theory for many years, so these find- 

 ings are of considerable fundamental significance. 

 Another new area of laser chemistry is that of las- 

 er-induced photodissociation, the basis for isotopic 

 selective photofragmentation, which is of intense 

 interest to the Energy Research and Development 

 Administration (ERDA) as a promising new tech- 

 nique for nuclear fuel enrichment. NBS has played 

 a major role in the basic research behind ERDA's 

 efforts. 



As to the future, the use of new tools, and espe- 

 cially of lasers, for studying excited atomic and 

 molecular states, and state-to-state transitions 

 between them is recognized nationally as a new 

 and scientifically exciting approach to developing 

 new concepts underlying chemical reactions, 

 broadly defined, and to finding powerful new in- 

 sights into all phenomena where atomic and mole- 

 cular processes are involved. The full exploitation 

 of the potential of atomic and molecular science 

 will require extensive collaboration by chemists 

 and physicists, and theory as well as experiment. 

 NBS is in an excellent position to play a major role 

 in the future unfolding of this significant field. 



Nuclear Science 



NBS has maintained research programs in nucle- 

 ar science from near its beginning, derived partly 

 from early involvement in radiation standards and 

 later in nuclear measurements. An example of re- 

 cent work at NBS is the precision measurement of 

 electron scattering at the NBS linear accelerator 

 (LINAC), in which NBS workers have collaborat- 

 ed with groups from numerous universities in this 

 country and abroad and from other agencies of 

 Government. Accurate hexadecapole measure- 

 ments of deformed heavy nuclei have provided 

 unique information on the radial charge distribu- 

 tion. 



A second example is the investigation of the 

 normal modes of the nucleus and the giant reso- 

 nance of the nuclear electric dipole. As early as 

 1965 theoreticians conjectured that the giant reso- 

 nance should couple into the quadrupole vibrations 

 of the nuclear surface. At NBS, calculations were 

 made of the expected cross sections, and the pre- 

 dicted effects were subsequently measured with 



plane polarized monochromatic 7-rays. Within the 

 limited precision available, photons were observed 

 to be scattered along the incident polarization vec- 

 tor, due to the coupling to the spherical vibrations, 

 while no scattering in this direction was measured 

 from the rigid spherical nucleus of -O'^Bi, as ex- 

 pected, in a beautiful confirmation of the theory. 

 Other theoretical work has also dealt with many 

 aspects of high energy electromagnetic reactions 

 ranging from radiation transport to few nucleon 

 dynamics and elementary particle interactions. 



In the near future NBS research on nuclear 

 structure will make two major thrusts. In the first, 

 improved experimental resolution of electron scat- 

 tering will be combined with improved counting 

 rates to allow the study of the more closely spaced 

 and weaker nuclear excited states. The second 

 thrust will use a monoenergetic photon beam ob- 

 tained from inflight annihilation of LINAC posi- 

 trons to study nuclei by means of elastic and ine- 

 lastic photon scattering. 



In the long term, further advances in under- 

 standing nuclear structure by means of electromag- 

 netic probes will demand detection of nuclear de- 

 cay products in coincidence experiments. These 

 experiments will require accelerators with a much 

 higher duty cycle than the present NBS LINAC. 



Thermal Studies of Matter 



NBS has for many years been in the forefront 

 of the study of the thermal properties of matter. 

 An international conference on critical phenome- 

 na, held at NBS in 1965, marked the beginning of a 

 mature understanding of that field. At this confer- 

 ence, the apparent universality of critical point 

 behavior was first clearly demonstrated. That is, 

 the behavior of a material near its critical point 

 was found to be independent of details such as 

 the atomic force laws, at least in a large variety of 

 cases. Research at NBS has concentrated on clar- 

 ifying and extending the universality concept by 

 making high precision measurements on fluids and 

 fluid mixtures near their critical points. 



Theoretical studies of liquid structure and spa- 

 tially disordered matter have led to a first-princi- 

 ples theory of first-order phase transitions (e.g., 

 melting-freezing), and has made possible for the 

 first time an investigation of the properties of 

 thermodynamically metastable states without in- 

 voking arbitrary and unjustified assumptions. 

 Computer simulation of shock waves in lattices is 

 being used to study the response of solids to 

 strong perturbations from thermal equilibrium. 



A principal challenge of much of this work on 

 the thermal properties of matter, which will con- 

 tinue to be addressed in the future, is dealing with 

 systems far from equilibrium, in nearly all analy- 

 ses of kinetic phenomena, one now assumes that 



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