Hi Dan, Take a look at the fit in q-space with the model below. I suspect that you have left out important Multiple scattering paths that would cause a miss-fit to the data at low k values. To test for this, change the fit range to something like 4.0 1/Anstroms for k-min value, and try again. Shelly

-----Original Message----- From: dmc@pdx.edu [mailto:dmc@pdx.edu] Sent: Friday, October 29, 2004 11:03 AM To: XAFS Analysis using Ifeffit Subject: RE: [Ifeffit] Fitting Commercial Molybdenum Disulfide

Hi Shelly,

I seperated the delr's with different alpha terms, but Mike seems to think that this is assuming isotropic expansion that isn't there. Also, the reduced chi-square has gone up 150 or so.

delr# define: alpha# * reff

Thanks for the help, Dan

Results with 1 eO and differing delr's:

Independent points = 14.312500000 Number of variables = 7.000000000 Chi-square = 6186.771083042 Reduced Chi-square = 846.054165202 R-factor = 0.031090393 Measurement uncertainty (k) = 0.000181935 Measurement uncertainty (R) = 0.004860095 Number of data sets = 1.000000000

Guess parameters +/- uncertainties (initial guess): ss = 0.0042720 +/- 0.0006590 (guessed as 0.004636 (0.000411)) e0 = 1.3293700 +/- 1.4673640 (guessed as 1.765958 (1.154388)) alpha = -0.0001750 +/- 0.0040010 (guessed as 0.001090 (0.002843)) ss2 = 0.0043180 +/- 0.0007370 (0.0000) ss3 = 0.0072300 +/- 0.0164390 (0.0000) alpha2 = 0.0076940 +/- 0.0027880 (0.0000) alpha3 = -0.0512670 +/- 0.0232140 (0.0000)

Def parameters: delr_1 = -0.0006930 delr_2 = 0.0305320 delr_3 = -0.2034430

Set parameters: amp = 0.7

Correlations between variables: e0 and alpha --> 0.8441 ss3 and alpha2 --> 0.7651 ss2 and alpha2 --> -0.6441 e0 and alpha2 --> 0.5682 ss2 and ss3 --> 0.4871 alpha and alpha2 --> 0.4785 ss3 and alpha3 --> 0.3825 e0 and alpha3 --> -0.2743 All other correlations are below 0.25

Original (2 e0s):

Independent points = 14.312500000 Number of variables = 6.000000000 Chi-square = 5778.957783654 Reduced Chi-square = 695.212966455 R-factor = 0.029041008 Measurement uncertainty (k) = 0.000181935 Measurement uncertainty (R) = 0.004860095 Number of data sets = 1.000000000

Guess parameters +/- uncertainties (initial guess): e0_1 = -4.0347670 +/- 2.9998980 (guessed as -4.072009 (1.919404)) ss = 0.0042860 +/- 0.0005990 (guessed as 0.004636 (0.000411)) e0 = 1.6770760 +/- 1.3230290 (guessed as 1.765958 (1.154388)) alpha = 0.0009180 +/- 0.0034050 (guessed as 0.001090 (0.002843)) ss2 = 0.0048160 +/- 0.0006910 (0.0000) ss3 = 0.0225310 +/- 0.0657250 (0.0000)

Def parameters: delr_1 = 0.0036440

Set parameters: amp = 0.7

Correlations between variables: e0_1 and alpha --> 0.8542 e0 and alpha --> 0.8470 e0_1 and e0 --> 0.7407 e0_1 and ss3 --> 0.7060 alpha and ss3 --> 0.4715 ss2 and ss3 --> -0.4214 e0_1 and ss2 --> -0.3892 e0 and ss3 --> 0.3772 alpha and ss2 --> -0.2680 All other correlations are below 0.25

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