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390( )F. Fillaux et al.rChemical Physics 244 1999 387–403Table 2Atom coordinates for potassium hydrogen maleateAtom xra yr b zrcKŽ. 1 0.2628Ž.3 0.7500 0.00000.2610Ž.2 0.7500 0.00000.2610Ž.3 0.7500 0.0000OŽ. 1 0.4842Ž. 2 0.2965Ž. 1 0.17391Ž.50.4895Ž. 1 0.29438Ž. 5 0.17376Ž.20.4894Ž. 2 0.2942Ž. 1 0.17376Ž.4OŽ. 2 0.2368Ž. 2 0.4195Ž. 1 0.07191Ž.60.23586Ž. 9 0.41932Ž. 6 0.07109Ž.20.2359Ž. 2 0.4194Ž. 1 0.07104Ž.4CŽ. 1 0.2824Ž. 1 0.3968Ž. 1 0.14745Ž.40.28292Ž. 8 0.39632Ž. 5 0.14694Ž.20.2828Ž. 1 0.39637Ž. 9 0.14691Ž.4CŽ. 2 0.0904Ž. 2 0.48852Ž. 9 0.20790Ž.50.08707Ž. 8 0.48966Ž. 5 0.20783Ž.20.0871Ž. 1 0.48989Ž. 9 0.20785Ž.4H21 Ž . y0.0744Ž. 4 0.5650Ž. 2 0.1767Ž.1y0.0813Ž. 2 0.5675Ž. 1 0.17664Ž.6y0.0809Ž. 4 0.5673Ž. 3 0.1767Ž.1HŽ. 1 0.4942Ž. 5 0.2939Ž.3 0.25000.4985Ž. 3 0.2919Ž.2 0.25000.4987Ž. 5 0.2921Ž.3 0.2500For each atom, the three rows are, from the top, the coordinates at300, 14 and 5 K.sample. There is a small component Ž Q .H and theneutron momentum polarisation is:< Q < 25 E0Rs ( Ž 12.< Q < EHfŽy1E and E 32 cm .0 f are the energies of the incidentand scattered neutrons, respectively. At low energyŽy1transfer, R is only moderate ;3 at 100 cm ..However, the polarisation improves rapidly, suchthat R;25 at 800 cm y1 . For large energy transfer,any influence of Q H can be ignored.The crystals wrapped in aluminium foil weremounted in a closed cycle refrigerator such that themomentum transfer component Q 5 was parallel tothe c crystal axis. For powders, about 3 g of sampleswere wrapped in aluminium foil and loaded into aclosed cycle refrigerator. For all samples, the temperaturewas Ž 20"2.K.Potential functions were calculated using basissets of 40 harmonic oscillator wave functions w34,35 x.INS intensities were calculated by numerical integraw36x:SŽ Q ,v . s
( )F. Fillaux et al.rChemical Physics 244 1999 387–403 391Table 4Thermal parameters Ž in A˚2units.for potassium hydrogen maleateŽ . Ž . Ž . Ž . Ž . Ž . Ž .Atom U 11 U 22 U 33 U 23 U 13 U 12 U isoKŽ. 1 0.0352Ž. 9 0.0350Ž. 9 0.0303Ž. 9 0.0011Ž.8 0.0000 0.0000 0.03340.0046Ž. 3 0.0054Ž. 3 0.0041Ž. 3 0.0001Ž.2 0.0000 0.0000 0.00470.0055Ž. 6 0.0051Ž. 7 0.0050Ž. 6 0.0004Ž.5 0.0000 0.0000 0.0052OŽ. 1 0.0433Ž. 5 0.0507Ž. 6 0.0261Ž. 7 y0.0023Ž. 4 0.0011Ž. 3 0.0150Ž.4 0.03710.0070Ž. 2 0.0079Ž. 2 0.0044Ž. 2 y0.0001Ž. 1 0.0001Ž. 1 0.0027Ž.1 0.00600.0081Ž. 3 0.0086Ž. 4 0.0040Ž. 3 y0.0002Ž. 2 y0.0002Ž. 2 0.0026Ž.3 0.0063OŽ. 2 0.0526Ž. 6 0.0481Ž. 6 0.0254Ž. 5 0.0020Ž. 5 y0.0050Ž. 3 0.0011Ž.4 0.03970.0082Ž. 2 0.0079Ž. 2 0.0037Ž. 2 0.0001Ž. 1 y0.0005Ž. 1 0.0008Ž.1 0.00610.0089Ž. 3 0.0081Ž. 3 0.0035Ž. 3 0.0002Ž. 2 y0.0005Ž. 2 0.0013Ž.2 0.0062CŽ. 1 0.0329Ž. 5 0.0308Ž. 5 0.0248Ž. 4 y0.0002Ž. 3 y0.0016Ž. 3 y0.0024Ž.3 0.02920.0055Ž. 1 0.0053Ž. 1 0.0037Ž. 1 y0.00018Ž. 9 y0.00005Ž. 8 0.00021Ž.9 0.00480.0062Ž. 3 0.0059Ž. 3 0.0032Ž. 3 y0.0004Ž. 2 y0.0001Ž. 2 0.0002Ž.2 0.0048CŽ. 2 0.0341Ž. 5 0.0333Ž. 5 0.0298Ž. 4 0.0011Ž. 3 y0.0022Ž. 3 0.0043Ž.3 0.03210.0061Ž. 1 0.0064Ž. 1 0.0042Ž. 1 0.00005Ž. 8 y0.00025Ž. 9 0.0014Ž.1 0.00540.0065Ž. 3 0.0073Ž. 3 0.0039Ž. 3 0.0001Ž. 2 y0.0002Ž. 2 0.0013Ž.2 0.0056HŽ 21. 0.066Ž. 1 0.068Ž. 1 0.051Ž. 1 0.0074Ž. 8 y0.0079Ž. 9 0.0264Ž.9 0.04800.0207Ž. 4 0.0254Ž. 4 0.0167Ž. 4 0.0025Ž. 3 y0.0031Ž. 3 0.0111Ž.3 0.01840.0214Ž. 7 0.0268Ž. 8 0.0170Ž. 7 0.0031Ž. 5 y0.0033Ž. 5 0.0119Ž.7 0.0187HŽ. 1 0.048Ž. 1 0.056Ž. 1 0.044Ž. 1 0.0000 0.0000 0.0139Ž.9 0.05640.0163Ž. 4 0.0183Ž. 5 0.0225Ž. 5 0.0000 0.0000 0.0030Ž.4 0.01870.0159Ž. 9 0.020Ž. 1 0.023Ž. 1 0.0000 0.0000 0.0034Ž.8 0.0193For each atom the three rows are, from the top, the thermal parameters at 300, 14 and 5 K.Temperature factors of all atoms decrease substantiallyŽ Table 4.and the decrease is larger for heavieratoms than for protons. Considering the maleateanion as a rigid body, excluding the hydrogen atoms,a thermal libration analysis w37xshows a large decreaseof libration, from "88 at room temperature to"38 at 5 and 14 K. The principal axis of libration isperpendicular to the maleate anion. Librational correctionsto heavy atom bond lengths are negligibleŽ no more than 0.001 A˚at low temperature .. Themaleate ion is virtually planar, with maximum deviationfrom the mean plane less than 0.01 A. ˚ Thethermal parameters for hydrogen bonding protonsHŽ. 1 and for protons bound to carbon atoms HŽ 21.are similar.of much better quality. These sharp bands are incontrast to infrared spectra. Above 2000 cm y1 , onlythe CH stretching modes are observed at ;3080cm y1 for the KHMH 2 and KDMH 2 derivatives. Theassignment scheme proposed in Table 5 is straightforward.Bands due to the three modes of the hydrogenbond dominate the spectra of the KHMD2sampleŽ Fig. 4 .. The oriented single crystal confirms that4. INS spectra and band assignmentThe INS spectra of powdered samples and alignedsingle crystals of KHMH Ž Figs. 2 and 3 .2 , KHMD2Ž Figs. 4 and 5. and KDMH Ž powder only, Fig. 6.2reveal well-resolved bands below 2000 cm y1 , ingeneral agreement with previous works w22,24 x, butFig. 2. INS spectrum of totally hydrogenated potassium hydrogenmaleate. Powdered sample at 20 K.
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