The derived imaginary parts of the refractive indices, k, for the MGS-1 sample using the model framework with GRS2 particle shapes as presented in Martikainen et al. 2023, ApJS. 

The real part of the refractive index, n, was fixed to 1.5.

The uncertainties were computed by assuming a maximum error of 15% in the measured reflectance over the 200 to 2000 nm wavelength range.

wavelength	k		error
200		0.000538		±0.00008
225		0.000644		±0.00009
250		0.000674		±0.00012
275		0.000644		±0.00009
300		0.000591		±0.00011
325		0.000549		±0.00009
350		0.000491		±0.00008
375		0.000452		±0.00008
400		0.000430		±0.00008
450		0.000414		±0.00008
500		0.000416		±0.00009
550		0.000416		±0.00008
600		0.000414		±0.00009
650		0.000433		±0.00010
700		0.000445		±0.00010
750		0.000460		±0.00011
800		0.000547		±0.00012
850		0.000687		±0.00014
900		0.000791		±0.00016
950		0.000831		±0.00017
1000		0.000819		±0.00017
1050		0.000801		±0.00017
1100		0.000787		±0.00017
1150		0.000802		±0.00017
1200		0.000811		±0.00018
1250		0.000831		±0.00020
1300		0.000850		±0.00020
1350		0.000880		±0.00019
1400		0.000889		±0.00022
1450		0.000909		±0.00022
1500		0.000938		±0.00021
1550		0.000968		±0.00023
1600		0.001019		±0.00024
1650		0.001056		±0.00024
1700		0.001095		±0.00025
1750		0.001124		±0.00025
1800		0.001153		±0.00028
1850		0.001192		±0.00028
1900		0.001212		±0.00028
1950		0.001212		±0.00031
2000		0.001212		±0.00028