Derivation of A′(H₂S). Left panel: HeNe laser interference pattern obtained from the growing H₂S ice at 10 K (black) together with its sinusoidal fitting (red). Changes in the amplitude of the fringes are attributed to laser instabilities. Right panel: Integrated absorbance area of the SH stretching mode of H₂S as a function of column density as derived from the fringe patter. A linear fit to the points is also shown in red.