Dear Silvio, I was not able to view the image, but what you are describing seems like the Ramsauer-Townsend effect (Phys Rev B, 1988, V38, 10919–10921). As far as I understand it, the physical interpretation is that the at the energy of the dip, the potential well of the scattering atom has cross- section that is very close to the wavelength of the photoelectron. Consequently, the photoelectron is not scattered back to the absorbing atom efficiently at this energy. Perhaps someone in the list can explain this more clearly (or correctly). Sincerely, Wayne Lukens On Nov 5, 2006, at 4:38 AM, levy@msri.org wrote:
Dear List,
I have noticed in several fits that Artemis -- i.e., feff -- reports for a SINGLE shell (with absorber = scatterer = Hg, edge = L3) an almost-node in the envelope of chi(k) around 6 inverse angstroms. See the image at
http://pjm.math.berkeley.edu/users/levy/files/HgNode.gif
and the FEFF output after my signature.
I've done my best to account for this behavior, but I simply don't have a physical intuition for why the F(k) factor should dip to zero or almost zero. Note that this is not a beat caused by two similar frequencies being added; the Fourier transform does of course show two peaks -- which is how my curiosity was aroused -- but the example figure comes from a SINGLE path, with 12 identical scatterers all at the same distance from the absorber.
Looking forward to your two cents...
Silvio
Metacinnabar from CSDWeb, HgS Niculescu et al. 1970 Feff 6L.02 potph 4.12 Abs Z=80 Rmt= 1.327 Rnm= 1.667 LIII shell Pot 1 Z=16 Rmt= 1.218 Rnm= 1.515 Pot 2 Z=80 Rmt= 1.310 Rnm= 1.624 Gam_ch=5.000E+00 H-L exch Mu=-2.727E+00 kf=1.809E+00 Vint=-1.519E+01 Rs_int= 2.005 Path 2 icalc 2 Feff 6L.02 genfmt 1.4\4
----------------------------------------------------------------------- -------\- 2 12.000 4.1366 2.9707 -2.72701 nleg, deg, reff, rnrmav(bohr), edge x y z pot at# 0.0000 0.0000 0.0000 0 80 Hg absorbing atom 0.0000 -2.9250 -2.9250 2 80 Hg k real[2*phc] mag[feff] phase[feff] red factor lambda real[p]@# 0.000 5.8876E+00 0.0000E+00 -5.3100E+00 0.1085E+01 5.5410E+00 1.8179E+00 0.200 5.8828E+00 6.5887E-02 -6.9020E+00 0.1085E+01 5.5726E+00 1.8284E+00 0.400 5.8685E+00 1.3063E-01 -8.3679E+00 0.1084E+01 5.6628E+00 1.8594E+00 0.600 5.8452E+00 1.9388E-01 -9.7059E+00 0.1082E+01 5.7987E+00 1.9101E+00 0.800 5.8135E+00 2.5592E-01 -1.0913E+01 0.1079E+01 5.9607E+00 1.9793E+00 1.000 5.7742E+00 3.1673E-01 -1.1989E+01 0.1077E+01 6.1257E+00 2.0656E+00 1.200 5.7279E+00 3.7510E-01 -1.2932E+01 0.1075E+01 6.2715E+00 2.1679E+00 1.400 5.6750E+00 4.2855E-01 -1.3742E+01 0.1074E+01 6.3832E+00 2.2854E+00 1.600 5.6157E+00 4.7354E-01 -1.4416E+01 0.1075E+01 6.4589E+00 2.4174E+00 1.800 5.5491E+00 5.0618E-01 -1.4949E+01 0.1076E+01 6.5142E+00 2.5639E+00 2.000 5.4733E+00 5.2301E-01 -1.5329E+01 0.1077E+01 6.5837E+00 2.7250E+00 2.200 5.3844E+00 5.2240E-01 -1.5543E+01 0.1078E+01 6.7192E+00 2.9013E+00 2.400 5.2972E+00 5.4699E-01 -1.5605E+01 0.1190E+01 4.9983E+00 3.0942E+00 2.600 5.3179E+00 5.7289E-01 -1.5987E+01 0.1239E+01 4.3905E+00 3.2252E+00 2.800 5.3348E+00 5.8762E-01 -1.6217E+01 0.1258E+01 4.1537E+00 3.3638E+00 3.000 5.3246E+00 5.9586E-01 -1.6383E+01 0.1257E+01 4.0743E+00 3.5096E+00 3.200 5.3065E+00 6.1650E-01 -1.6474E+01 0.1250E+01 4.0802E+00 3.6618E+00 3.400 5.2733E+00 6.3374E-01 -1.6567E+01 0.1239E+01 4.1398E+00 3.8197E+00 3.600 5.2309E+00 6.4470E-01 -1.6663E+01 0.1226E+01 4.2364E+00 3.9827E+00 3.800 5.1752E+00 6.3603E-01 -1.6766E+01 0.1212E+01 4.3604E+00 4.1501E+00 4.000 5.1090E+00 6.0562E-01 -1.6883E+01 0.1198E+01 4.5058E+00 4.3214E+00 4.200 5.0331E+00 5.5941E-01 -1.6984E+01 0.1183E+01 4.6683E+00 4.4959E+00 4.400 4.9489E+00 4.9872E-01 -1.7115E+01 0.1168E+01 4.8452E+00 4.6734E+00 4.600 4.8588E+00 4.2625E-01 -1.7230E+01 0.1154E+01 5.0343E+00 4.8533E+00 4.800 4.7653E+00 3.5048E-01 -1.7327E+01 0.1139E+01 5.2341E+00 5.0355E+00 5.000 4.6691E+00 2.7395E-01 -1.7453E+01 0.1125E+01 5.4434E+00 5.2195E+00 5.200 4.5722E+00 1.9793E-01 -1.7590E+01 0.1110E+01 5.6610E+00 5.4051E+00 5.400 4.4760E+00 1.3243E-01 -1.7866E+01 0.1096E+01 5.8864E+00 5.5922E+00 5.600 4.3817E+00 8.0754E-02 -1.8387E+01 0.1083E+01 6.1187E+00 5.7805E+00 5.800 4.2890E+00 7.7722E-02 -1.9408E+01 0.1070E+01 6.3576E+00 5.9699E+00 6.000 4.1996E+00 1.2225E-01 -1.9952E+01 0.1058E+01 6.6024E+00 6.1603E+00 6.500 3.9822E+00 2.6906E-01 -2.0350E+01 0.1031E+01 7.2385E+00 6.6398E+00 7.000 3.7681E+00 3.8170E-01 -2.0473E+01 0.1010E+01 7.9052E+00 7.1233E+00 7.500 3.5495E+00 4.3899E-01 -2.0529E+01 0.9919E+00 8.5988E+00 7.6098E+00 8.000 3.3245E+00 4.4840E-01 -2.0549E+01 0.9763E+00 9.3169E+00 8.0987E+00 8.500 3.1062E+00 4.3705E-01 -2.0526E+01 0.9613E+00 1.0057E+01 8.5893E+00 9.000 2.8953E+00 4.1495E-01 -2.0476E+01 0.9480E+00 1.0818E+01 9.0814E+00 9.500 2.6939E+00 3.9247E-01 -2.0391E+01 0.9367E+00 1.1598E+01 9.5746E+00 10.000 2.4999E+00 3.7170E-01 -2.0271E+01 0.9291E+00 1.2396E+01 1.0069E+01 11.000 2.1169E+00 3.6890E-01 -1.9990E+01 0.9196E+00 1.4041E+01 1.1059E+01 12.000 1.7611E+00 4.1306E-01 -1.9816E+01 0.9119E+00 1.5747E+01 1.2052E+01 13.000 1.4328E+00 4.6749E-01 -1.9744E+01 0.9072E+00 1.7507E+01 1.3046E+01 14.000 1.1169E+00 5.1022E-01 -1.9760E+01 0.9054E+00 1.9317E+01 1.4041E+01 15.000 8.2534E-01 5.3666E-01 -1.9821E+01 0.9032E+00 2.1172E+01 1.5037E+01 16.000 5.5314E-01 5.4489E-01 -1.9903E+01 0.9025E+00 2.3070E+01 1.6034E+01 17.000 2.9163E-01 5.3763E-01 -2.0012E+01 0.9015E+00 2.5007E+01 1.7031E+01 18.000 4.7223E-02 5.2008E-01 -2.0124E+01 0.8986E+00 2.6981E+01 1.8029E+01 19.000 -1.8906E-01 4.9327E-01 -2.0255E+01 0.8968E+00 2.8989E+01 1.9027E+01 20.000 -4.1335E-01 4.6035E-01 -2.0384E+01 0.8947E+00 3.1029E+01 2.0025E+01
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