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.