Conformers of the α-Pinene···Water Complex and Their Atmospheric Impacts: Insights from Rotational Spectroscopy

Biogenic volatile organic compounds such as α-pinene significantly influence atmospheric chemistry and secondary organic aerosol formation. Through broadband chirped pulse Fourier transform microwave spectroscopy and electronic structure calculations, we identified two conformers of the α-pinene···water complex, differentiated by the position of the water molecule relative to the π-bond of α-pinene. Dihedral angle energy scans revealed shallow minima with low barriers, suggesting rotational flexibility of the water molecule about the O-H···π bond. Classical transition state theory calculations demonstrate that hydration lowers the activation energy for α-pinene ozonolysis, leading to a significant increase in the bimolecular rate constant. Given the substantial atmospheric emissions of α-pinene, the formation of α-pinene···water complexes could enhance its reactivity with ozone, influencing secondary organic aerosol formation and other atmospheric processes. This study provides a detailed structural and dynamical analysis of the α-pinene···water complex, offering insights into the unique intermolecular interactions present and their potential impact on atmospheric chemistry.