DURING a balloon flight on December 7, 1967, the infrared solar spectrum in the region from 6.2 µm to 10.0 µm was monitored from 30 km as the Sun set. The spectra obtained during this period revealed the strong enhancement of a previously unidentified absorption feature at 1,325.7 cm−1, and examination indicated that this feature was the Q branch of a polyatomic molecule. The P and R branches were also present but the instrument resolution (0.2 cm−1) was not sufficient to resolve the rotational structure.