  Characterizing the photolysis processes undergone by transient volatile
organic compounds in the troposphere requires the knowledge of their
photoabsorption cross-section - quantities often challenging to determine
experimentally, particularly due to the reactivity of these molecules. We
present a computational tool coined AtmoSpec, which can predict a quantitative
photoabsorption cross-section for volatile organic compounds by using
computational photochemistry. The user enters the molecule of interest as a
SMILES code and, after selecting a level of theory for the electronic structure
(and waiting for the calculations to take place), is presented with a
photoabsorption cross-section for the low-energy conformers and an estimate of
the photolysis rate coefficient for different standardized actinic fluxes. More
specifically, AtmoSpec is an automated workflow for the nuclear ensemble
approach, an efficient technique to approximate the absolute intensities and
excitation wavelengths of a photoabsorption cross-section for a molecule in the
gas phase. This work provides background information on the nuclear ensemble
approach, a guided example of a typical AtmoSpec calculation, details about the
architecture of the code, and the current limitations and future developments
of this tool.
