We present laboratory measurements of the absorption cross sections of the &ngr;5 band (540--580 cm-1) of chlorine nitrate made under stratospheric conditions of temperature and pressure. We use the measured cross sections and observed mid-infrared stratospheric emission spectra to retrieve mid-latitude vertical mixing ratio profiles for both day and night in the altitude range 20--34 km, and compare the results with a sunset profile obtained simultaneously from solar absorption measurements of the &ngr;4 Q branch at 780 cm-1. The profiles obtained using these two methods are shown to be in excellent agreement, validating retrievals using the &ngr;4 band. We also find good agreement in this altitude range between the observed day/night ratio and the results of a 1-D photochemical model. ¿ American Geophysical Union 1996