AtmoSpec -- A Tool to Calculate Photoabsorption Cross-Sections for Atmospheric Volatile Organic Compounds

TL;DR

AtmoSpec is a computational tool that predicts photoabsorption cross-sections of atmospheric volatile organic compounds, aiding in understanding their photolysis processes without experimental measurements.

Contribution

This work introduces AtmoSpec, an automated workflow using the nuclear ensemble approach to estimate photoabsorption cross-sections for VOCs from molecular structure inputs.

Findings

Provides photoabsorption cross-sections for various VOCs

Estimates photolysis rate coefficients under different fluxes

Demonstrates the tool's application with a guided example

Abstract

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.