We have determined the real and imaginary indices of refraction (n and k) for six iron oxide/oxyhydroxide phases - magnetite, maghemite, goethite, lepidocrocite, akaganéite, and ferrihydrite. A single crystal of magnetite was used to derive bulk n and k values from 100-2000 cm-1. Synthetic nanocrystalline samples of maghemite, goethite, lepidocrocite, akaganéite, and ferrihydrite were pressed into compact pellets used to determine bulk n and k values from 100-1200 cm-1. All values of n and k (the optical constants) were determined from specular reflectance spectra acquired at 2 cm-1 spectral sampling using classical Lorentz-Lorenz dispersion theory. In this paper, we present the optical constants of all six minerals and the oscillator parameters with which they were modeled. Use of these optical constants could aid in radiative transfer models of terrestrial dust as well as Mars, the Moon, and other airless bodies in the solar system
Oscillator parameters for magnetite and goethite
|
Magnetite MAG1 |
Goethite GTS2 |
||||
|
ε0=4.1778 |
ε0=2.4991 |
||||
|
ν (cm-1) |
γ |
4πρ |
ν (cm-1) |
γ |
4πρ |
|
135 |
2.1764 |
33.8797 |
268 |
0.0505 |
0.3974 |
|
268 |
1.1106 |
8.9758 |
276 |
0.0501 |
0.2610 |
|
293 |
0.1477 |
0.3104 |
287 |
0.0507 |
0.1343 |
|
336 |
0.1564 |
0.7450 |
297 |
0.0433 |
0.0612 |
|
344 |
0.0623 |
0.1154 |
353 |
0.0587 |
0.0506 |
|
431 |
0.0678 |
0.0620 |
374 |
0.0596 |
0.1248 |
|
462 |
0.1635 |
0.2123 |
398 |
0.0579 |
0.4917 |
|
532 |
0.1922 |
0.4379 |
420 |
0.1008 |
0.3504 |
|
559 |
0.0819 |
0.2582 |
454 |
0.0591 |
0.0375 |
|
612 |
0.0855 |
0.0486 |
466 |
0.1513 |
0.2845 |
|
635 |
0.0402 |
0.0116 |
582 |
0.0470 |
0.0065 |
|
692 |
0.1031 |
0.0433 |
608 |
0.1108 |
0.0842 |
|
770 |
0.3523 |
0.2357 |
632 |
0.0426 |
0.0032 |
|
1049 |
0.7096 |
0.6783 |
674 |
0.0590 |
0.0085 |
|
1747 |
1.0689 |
1.1531 |
799 |
0.0391 |
0.0765 |
|
|
|
|
895 |
0.0328 |
0.0215 |
|
|
|
|
909 |
0.0265 |
0.0130 |
Oscillator parameters for
lepidocrocite and akaganéite
|
Lepidocrocite LPS2 |
Akaganéite AKG1 |
||||
|
ε0=2.5969 |
ε0=3.0708 |
||||
|
ν (cm-1) |
γ |
4πρ |
ν (cm-1) |
γ |
4πρ |
|
223 |
0.0469 |
0.1051 |
248 |
0.0645 |
0.1299 |
|
259 |
0.0633 |
0.1094 |
264 |
0.0953 |
0.4801 |
|
269 |
0.0732 |
0.2138 |
280 |
0.1438 |
0.3406 |
|
281 |
0.1082 |
0.3026 |
360 |
0.1831 |
0.5851 |
|
356 |
0.0968 |
0.3569 |
390 |
0.1625 |
0.8689 |
|
379 |
0.3821 |
1.1177 |
436 |
0.1745 |
0.2533 |
|
467 |
0.1057 |
0.2312 |
475 |
0.1411 |
0.2250 |
|
504 |
0.0637 |
0.0297 |
637 |
0.0847 |
0.1101 |
|
524 |
0.1306 |
0.1102 |
668 |
0.0650 |
0.0689 |
|
602 |
0.1520 |
0.0927 |
692 |
0.0762 |
0.0922 |
|
748 |
0.0464 |
0.0228 |
786 |
0.0762 |
0.0116 |
|
895 |
0.0281 |
0.0008 |
854 |
0.0944 |
0.0552 |
|
1023 |
0.0229 |
0.0181 |
|
|
|
|
1154 |
0.0798 |
0.0113 |
|
|
|
Oscillator
parameters for
maghemite and ferrihydrite
|
Maghemite ISK1 |
Ferrihydrite FHYD2 |
||||
|
ε0=2.7679 |
ε0=1.9390 |
||||
|
ν (cm-1) |
γ |
4πρ |
ν (cm-1) |
γ |
4πρ |
|
212 |
0.0278 |
0.0237 |
260 |
0.4766 |
0.3521 |
|
234 |
0.0391 |
0.0646 |
321 |
0.3371 |
0.1888 |
|
258 |
0.9621 |
0.5464 |
390 |
0.3446 |
0.1695 |
|
262 |
0.0368 |
0.0779 |
462 |
0.3353 |
0.4057 |
|
275 |
0.0171 |
0.0033 |
597 |
0.2328 |
0.1218 |
|
282 |
0.0200 |
0.0046 |
692 |
0.1944 |
0.0681 |
|
288 |
0.0365 |
0.0169 |
830 |
0.1354 |
0.0075 |
|
309 |
0.0877 |
0.3155 |
930 |
0.1581 |
0.0148 |
|
327 |
0.0319 |
0.0486 |
|
|
|
|
349 |
0.0580 |
0.0853 |
|
|
|
|
366 |
0.0613 |
0.1398 |
|
|
|
|
393 |
0.0621 |
0.2475 |
|
|
|
|
419 |
0.0581 |
0.0573 |
|
|
|
|
442 |
0.0789 |
0.1597 |
|
|
|
|
465 |
0.0279 |
0.0080 |
|
|
|
|
476 |
0.0285 |
0.0132 |
|
|
|
|
485 |
0.0468 |
0.0442 |
|
|
|
|
526 |
0.0846 |
0.0688 |
|
|
|
|
552 |
0.0629 |
0.2162 |
|
|
|
|
584 |
0.0484 |
0.0525 |
|
|
|
|
608 |
0.0635 |
0.0722 |
|
|
|
|
635 |
0.0408 |
0.0549 |
|
|
|
|
645 |
0.1110 |
0.0658 |
|
|
|
|
691 |
0.0259 |
0.0121 |
|
|
|
|
702 |
0.0550 |
0.0290 |
|
|
|
|
729 |
0.0296 |
0.0079 |
|
|
|