[Ifeffit] fitting of S XANES with arctans and gaussians

[Matthew Marcus]

I'm trying to fit 37 micro-XANES spectra taken at the S K-edge, using the method discussed in the paper by Manceau and Nagy "Quantitative analysis of sulfur functional groups
in natural organic matter by XANES spectroscopy", Geochimica et Cosmochimica Acta 99 (2012) 206–223.  In this paper, they fit spectra to two arctangents and 6 gaussians,
with widths of the arctans slaved together and widths of gaussians 1-3 and 4-6 slaved (or all 6 to one value).  I'm looking for recommendations as to how to do the fit.
They give prescriptions for how to set the initial estimates to give robust values.  Manceau has told me that 'Athena works quite well', but I don't see any obvious way there
to do the parameter constraints called for, or to keep peak heights from going negative.  Athena also has a habit of assuming you want it to do the normalization
for you; I've already done that and need no further 'help'.  Any ideas?

I've tried using Genplot, but that offers no way to restrain parametsrs to ranges to keep them from going nuts.

PCA seems to want 6-8 components, so it's not all that helpful.  These spectra were taken at various spots on a biological structure (abalone radula) so there's
no sense of sequence which would enable the use of evolving factor analysis or something like that.  LCF doesn't give satisfying fits with the references I have.

I've attached a couple of the files, truncated to the range Manceau&Nagy fit to.  The originas were taken over the range 2460-2550eV.
	mam
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2459.8733	0.016383041
2460.1233	0.016094189
2460.3735	0.022025956
2460.6238	0.016678091
2460.8738	0.016311111
2461.124	0.019483142
2461.3743	0.01770903
2461.6245	0.022848981
2461.8745	0.018562062
2462.1248	0.020740321
2462.3748	0.020652939
2462.625	0.017123673
2462.8752	0.025094582
2463.1252	0.019867383
2463.3755	0.022139577
2463.6257	0.023213524
2463.8757	0.020676881
2464.126	0.025052877
2464.3762	0.029113997
2464.6262	0.026324339
2464.8765	0.023671083
2465.1267	0.028306101
2465.3767	0.026002042
2465.627	0.030652333
2465.8772	0.028775895
2466.1272	0.032816786
2466.3774	0.033937715
2466.6277	0.032948535
2466.8777	0.034721162
2467.1279	0.035310403
2467.3782	0.044202648
2467.6282	0.038343795
2467.8784	0.044291645
2468.1287	0.045460965
2468.3787	0.051915355
2468.6289	0.064561076
2468.8789	0.064293481
2469.1292	0.06745372
2469.3794	0.076904655
2469.6294	0.078936517
2469.8794	0.083785988
2470.1292	0.09224768
2470.3789	0.10311307
2470.6287	0.12705681
2470.8784	0.15507881
2471.1279	0.19775756
2471.3777	0.24674262
2471.6274	0.38095856
2471.8772	0.61600226
2472.127	0.95312738
2472.3767	1.3190417
2472.6262	1.579319
2472.876	1.6359525
2473.1257	1.5544981
2473.3755	1.4989064
2473.6252	1.5021619
2473.875	1.5229028
2474.1245	1.4984316
2474.3743	1.3305453
2474.624	1.0569189
2474.8738	0.83871508
2475.1235	0.74043173
2475.3733	0.70619929
2475.6228	0.73935717
2475.8726	0.8194145
2476.1223	0.87513489
2476.3721	0.88144314
2476.6218	0.90261424
2476.8716	0.89132398
2477.1211	0.89018643
2477.3708	0.8967182
2477.6206	0.90281725
2477.8704	0.94701087
2478.1201	0.94702822
2478.3699	0.97867304
2478.6194	1.0008969
2478.8691	1.0092386
2479.1189	1.0287796
2479.3687	1.08442
2479.6184	1.1615053
2479.8679	1.3039225
2480.1179	1.5145243
2480.3674	1.797269
2480.6172	2.0798359
2480.8669	2.2775149
2481.1167	2.3608608
2481.3662	2.3488405
2481.616	2.2907579
2481.8657	2.2880797
2482.1155	2.3719938
2482.3652	2.5308979
2482.615	2.589304
2482.8645	2.5814075
2483.1143	2.3856504
2483.364	2.1799946
2483.6138	1.9504212
2483.8635	1.7527013
2484.1133	1.5563732
2484.3628	1.4446132
2484.6125	1.3397398
2484.8623	1.2488514
2485.1121	1.2062074
2485.3618	1.141425
2485.6116	1.1280848
2485.8611	1.0882412
2486.1108	1.0844127
2486.3606	1.0722013
2486.6104	1.0759245
2486.8601	1.050091
2487.1099	1.0626349
2487.3596	1.0662534
2487.6091	1.0521868
2487.8589	1.0660895
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2459.8232	0.0086620357
2460.0735	0.0090417974
2460.3235	0.033545561
2460.5737	0.0085842237
2460.824	0.0051017846
2461.074	0.011186908
2461.3242	0.017373042
2461.5742	0.015282798
2461.8245	0.020608777
2462.0747	0.030159647
2462.3247	0.037008617
2462.575	0.019812036
2462.825	0.017694598
2463.0752	0.021219229
2463.3252	0.025639383
2463.5754	0.022631068
2463.8257	0.014809187
2464.0757	0.016797649
2464.3259	0.020190042
2464.5759	0.015993463
2464.8262	0.023149636
2465.0764	0.025470076
2465.3264	0.019795895
2465.5767	0.026845468
2465.8267	0.018706912
2466.0769	0.033239357
2466.3269	0.034196496
2466.5771	0.025028745
2466.8274	0.034550779
2467.0774	0.039939508
2467.3276	0.025766766
2467.5776	0.042343114
2467.8279	0.023223488
2468.0779	0.048359003
2468.3281	0.040589523
2468.5784	0.043160751
2468.8284	0.051982671
2469.0786	0.059320733
2469.3286	0.077092245
2469.5789	0.065575883
2469.8289	0.082144961
2470.0784	0.070433557
2470.3281	0.084788643
2470.5779	0.10309343
2470.8274	0.11019815
2471.0771	0.13859501
2471.3269	0.19976343
2471.5767	0.25412217
2471.8264	0.34704304
2472.0759	0.54530066
2472.3257	0.78615826
2472.5754	1.0521393
2472.8252	1.2056561
2473.0747	1.3237689
2473.3245	1.4084748
2473.5742	1.4852122
2473.824	1.5177881
2474.0735	1.4640881
2474.3232	1.3413973
2474.573	1.1608815
2474.8228	1.008761
2475.0725	0.8627153
2475.322	0.85124922
2475.5718	0.86840338
2475.8213	0.90438408
2476.071	0.96190357
2476.3208	0.98449355
2476.5706	0.95443678
2476.8203	0.94638139
2477.0698	0.89626169
2477.3196	0.85532951
2477.5693	0.8831256
2477.8191	0.88665426
2478.0686	0.90146577
2478.3184	0.92120427
2478.5681	0.90238905
2478.8179	0.94114095
2479.0674	1.0159788
2479.3171	1.0523196
2479.5669	1.1367817
2479.8167	1.2791884
2480.0664	1.501315
2480.3159	1.8128476
2480.5657	2.2177896
2480.8152	2.4746833
2481.0649	2.6505656
2481.3147	2.7177446
2481.5645	2.7476342
2481.8142	2.9169872
2482.0637	3.0258553
2482.3135	3.2625239
2482.5632	3.2067261
2482.813	3.0880082
2483.0625	2.8586359
2483.3123	2.5289466
2483.562	2.2037165
2483.8118	1.9437176
2484.0613	1.7121388
2484.311	1.5392073
2484.5608	1.4665928
2484.8105	1.365666
2485.0603	1.2651333
2485.3098	1.2447017
2485.5596	1.2118043
2485.8091	1.1773263
2486.0588	1.1215008
2486.3086	1.1032519
2486.5583	1.0873834
2486.8081	1.0994042
2487.0576	1.100813
2487.3074	1.0825663
2487.5571	1.0809017
2487.8069	1.0712752