Optical data on cryogenic ices

N2 Grundy, Schmitt, and Quirico 1993, Icarus 105, 254-258.
H2O Grundy and Schmitt 1998, J. Geophys. Res. 103, 25,809-25,822.
CH4 Grundy, Schmitt, and Quirico 2002, Icarus 155, 486-496.
CH3D Grundy et al. 2011, Icarus 212, 941-949.

Lots more are on the way...