Crystals of a high-pressure form of benzene (benzene 11) were grown in the diamond-anvil pressure cell at elevated temperature and pressure from the transition of solid I to solid II. X-ray precession data were obtained from a single-crystal in the high-pressure cell. At 21 degrees C and about 25 kilobars, benzene II crystallizes in the monoclinic system with a = 5.417 +/- 0.005 angstroms (S.D.), b = 5.376 +/- 0.019 angstroms, c = 7.532 +/- 0.007 angstroms, beta = 110.00 degrees +/- 0.08 degrees , space group P2(1)/ c, Pc= 1.26 grams per cubic centimeter. The crystal structure was solved by generating all possible molecular packing configurations and calculating structure factors, reliability factors, and packing energies for each configuration. This procedure produced a unique solution for the molecular packing of benzene II.

The infrared sp ectra of coesite, low-temperature tridymite, low-temperature cristobalitelow-~emperature quartz, vitreous silica, hexagonal Oe02, tetragonal Ge02, and vitreous germallla are reported from ~,OO O to 300 C~-l. Wherever possible an assignment of frequencies has been made on t he basls of the selectlOn rules for the crystal symmetry. Three characteris.tic gro up frequencies. near 1,lOq, 800, and 480 cm-1 are common to all the polymorphs of Sl02. Thes.e frequ~nCle.s respectlvely correspond to a str~tching mode i nvolving displacements assoclated prnnanly wlth the oxygen atoms, a stretclung mode involving displacements associated primarily . wi~h the. sil~co~ atoms, and a Si-O bending mode. The presence of these gro up frequencles III coeslte mdlcates that t he coordination of silicon in coesite is tetrahedral and that its high density is associated with the packinrr of tetrahedral units at an angle approximatiI?g 120 degrees.. The tetragonal and hexagon~l GC02 polymorphs show a marked dlfference III spectra due III part to the change from sixfold to fourfold coordination. The assignment of obscrved frequencies in hexagonal Ge02 is consistent with that made for low-temperature quartz if allowance is made for the heavier mass of t he Ge atom.

Infrared absorption spectra have been obtained on the alk ali nitrates, the divalent m etal carbonates, a nd t he rare eart h borates which assume t he aragoni te, calcitc, or vaterite cr ystal struct ures. It was observed t hat simi lar str uct ures gi ve rise to analogo us spectra except for t he carbonate and borates having the vaterite str uct ure. The marked differences o~scr~e d in t hese latter spectra. a re disc ussed. Frequency s hifts produ ced by cation s ubs t ltutlOn are ascnbed to repulslOn between closed electro n shells of oxyge n atoms . It is concluded t h at t his repulsive force determines the s tru cture type in the rare earth b~rates .

.Infrar ed abso rp t ion spectra of a n h ydr ou s, crystalline, ino rgani c borates were obtained lLl ~h e .2000 cm-I to 300 cm-I ra n ge. Compounds wit h B'O a nd B " isoto pes we re prepa red to ass Ist lI1 terpr etatlOn . Spectra l bands for all or t hobo rates and py roborates a nd som e meLaborates could be assign ed sat isfacto rily . Borates wit h complex rin g-ty p e an ion s gener a lly e~'(hlbl te d spectra of su ch co mplex ity t hat on ly s u perfi cial in terp retatio n WItS attempLed. }< rom correlatlOlI s between s pectra a nd stru cture It a ppears t hat boro n in 3-fold or in 4-fold coordin at ion can be iden t ifi ed wi t h r easo nable ass uran ce on t he bas is of t he infrared s pectrum alon e. Absorp t ion bands ar c ta,bulated for about 80 bo rates a lld typ ical sp ectra a rc s hown .

A p ress ure ce ll ,--as constructed usin g a pair of type II d ia monds for sL ud y of infrare d spectra of solids in t he 1-to l5-micro n reg ion . Usin g co mme rcia l infra red equipme nt, spectra can be st ud ied routin ely to calculated press ures as high a s 30 ,000 atm osphe res. U nde r pressure, bands ge nerall y shif t to higher fr eque ncies a nd decrease in in ten s ity. The m agni t ude of bo th cha nges dep ends on the mode of vib ra t ion. Occasion a ll y m ajor cha nges in s pectra occur. In calcite the carbon -oxyge n symme t ri c st retchin g, m od e v" becomes a cti ve a t ele vated press ures while the do ubly dege nera te V3, sLretching, < Ind "4, bend ing, f,' (,-quencies spl it . F l'Om t he s hi ft in frequency of v, wiLh pr e~s ure the " compressibil it..v", [( -l / R o)(dR/dp)]' of the C-O bo nd le ngth, R, is calcula ted to bp 2.8 X IO-7/ atm os phere. :'Iia:i or spec tral ch a nges are no t observed in the sa me press ure ranges in other car bonates hav ing the calcite or aragonit e s t r uctu res. Thc rCR ult s for calcit e may be expla in ed by a shif t of the COs ion fr om the trigo na l axi s und e ,' press ure.