@database PhysUPDATE.330.doc @remark Converted with HTML2Guide ©1997 Mark Harman @wordwrap @node MAIN "PhysUPDATE.330.doc" Date: Thu, 17 Jul 97 14:52:40 EDTFrom: physnews@aip.org (AIP listserver)To: physnews-mailing@aip.orgSubject: update.330PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics NewsNumber 330 July 17, 1997 by Phillip F. Schewe and Ben SteinAMORPHOUS SOLID WATER (ASW) is a flash-frozen, non-crystalline form of water which occurs when water vapor strikes avery cold (below 140 K) surface. Although this disorderly ice doesnot exist naturally on Earth, it may well constitute the vast majorityof water in the universe, where conditions are mostly chillier than140 K. For this reason, and because ASW represents a sort ofcompletely-slowed-down version of liquid water, scientists at thePacific Northwest National Lab (Bruce Kay, 509-376-0028, bd_kay@pnl.gov) have studied amorphous ice in their lab. Theyassemble an ASW layer atop a thin film of carbon tetrachloride(cleaning fluid). When the sample is warmed above 140 K, thewater molecules start to follow their hexagonal instincts byrestructuring themselves into a crystalline form. The initial stagein this process is the formation of tiny randomly oriented icecrystals. As more of these crystals form, the icy overlayer starts toresemble a layer of crushed ice, and the CCl4 molecules, with ahigh vapor pressure and eager to escape any way they can, start topercolate through the gaps between the grains. Following a mazeof branching pathways, the molecules eventually come to the ASWsurface and exit as "molecular volcanoes," analogous to the violentemergence of underground magma through fissures during avolcano. This line of research might have a bearing on the episodicrelease of gas from comets and other celestial bodies. (R. ScottSmith et al., upcoming article in Physical Review Letters; see thefigure at www.aip.org/physnews/graphics)A PRESSURE STANDARD FROM QUANTUM-MECHANICALSOUNDS may be possible, Berkeley researchers reported at lastmonth's Acoustical Society of America meeting. Applying pressureto a superfluid--an ultra cold liquid with zero resistance to flow--cancause it to move through a tiny hole and emit sounds at acharacteristic frequency. The sound is created when the superfluidsheds energy in the form of "quantum vortices" whose size andother properties depend on precisely known quantum mechanicalconstants. The Berkeley physicists, who recently used helium-4superfluids to measure the Earth's rotation rate (Update 318), saidtheir setup can potentially determine pressure from the soundfrequency if they can minimize temperature fluctuations whichcreate additional unwanted vortices. (ScienceNOW, June 18,1997).THE STEREODYNAMICS OF MOLECULES, the orientation andmovement of molecules in three-dimensional space, plays a largerole in chemical reactions. As with cosmonauts approaching theirspace station, some maneuvers are more effective than others inproducing a successful docking. In the case of diatomic hydrogenmolecules approaching a copper surface, an IBM Almaden/UCSanta Barbara collaboration has shown that the molecules have amuch better chance of crash landing and then sticking to the surfaceif the plane of the molecule (traced out by the mutual orbit of thetwo atoms about each other) is parallel to the surface. The reactionprocess was also observed to favor certain molecule kinetic energiesover others. Quantitative studies of stereo preferences should leadto a better understanding of catalysis and other industriallyimportant processes where chemical reactions are influenced bynearby surfaces. (H. Hou et al., Science, 4 July 1997.) @endnode