Stratospheric observation of far IR pure rotational lines of hydroxyl

Abstract

The hydroxyl radical, OH, has a key role in many atmospheric and ionospheric processes and has been detected in molecular clouds in space. The well-known near IR vibration–rotation bands of this molecule, named after their discoverer, Meinel, were first identified in atmospheric observations¹ while much of the impetus for precise microwave data has come from the identification of radiation in this wavelength range from OH in space². However, although increasingly precise measurements have now been reported from the UV³ through the IR⁴ to the microwave spectral regions⁵, the far IR pure rotational line spectrum has been virtually ignored, and no observations of this relatively simple spectrum have been reported between 5 and 500 cm⁻¹. Here we present measurements of spectra between 30 and 110 cm⁻¹ and deduce stratospheric OH column densities from the observed spectral lines.