Establishing an accurate infrared band strength for the cyanate ion in interstellar ices

ABSTRACT A prominent infrared (IR) spectral feature near 2165 cm−1 (λ = 4.62 $\mu$m) in interstellar ices has been attributed to the cyanate ion (OCN−) for almost 40 yr, but firm, first-principles solid-phase IR data for quantifying IR-astronomical observations of OCN− in a H2O-rich amorphous ice have never been published. Here we report the first laboratory study that delivers such an IR band strength for OCN− that is reproducible and free of ambiguous uncertainties concerning ice density, thickness, and temperature, providing new quantitative results for both observational and laboratory astronomers. Additional results include the first robust measurements of IR band strengths of isocyanic acid (HNCO), ammonia (NH3), and the ammonium ion (NH4+) in H2O-rich ice.