ExoMol molecular line lists - XI. The spectrum of nitric acid

Abstract

Nitric acid is a possible biomarker in the atmospheres of exoplanets. An accurate line list of rotational and rotational-vibrational transitions is computed for nitric acid (HNO3). This line list covers wavelengths longer than 1.42 μm (0-7000 cm-1) and temperatures up to 500 K. The line list is computed using a hybrid variational - perturbation theory and empirically tuned potential energy and dipole surfaces. It comprises almost seven billion transitions involving rotations up to J = 100. Comparisons with spectra from the HITRAN and Pacific Northwest National Laboratory data bases demonstrate the accuracy of our calculations. Synthetic spectra of water-nitric acid mixtures suggest that nitric acid has features at 7.5 and 11.25 μm that are capable of providing a clear signature for HNO3; the feature at 11.25 μm is particularly promising. Partition functions plus full line lists of transitions are made available in an electronic form as supplementary data to the article and at www.exomol.com.