In the present work, how the non-Rice–Ramsperger–Kassel–Marcus (RRKM) effect evolves in going from gas-phase HO3•$\text{HO}_{3}^{\cdot}$ to microsolvated HO3•$\text{HO}_{3}^{\cdot}$ is investigated. These investigations reveal that as the number of water molecules in HO₃··(H₂O) _n increases, the non-RRKM effect decreases.

Hydrotrioxyl radical (HO3•$\text{HO}_{3}^{\cdot}$) is proposed as a transient species in various important atmospheric reactions. One factor that can influence the lifetime of HO3•$\text{HO}_{3}^{\cdot}$ in the atmosphere is its ability to form complexes with water monomers and dimers, i.e., microsolvated systems. In addition, a recent study suggests that the lifetime of HO3•$\text{HO}_{3}^{\cdot}$ is greatly influenced by the non-Rice–Ramsperger–Kassel–Marcus (RRKM) effect, and hence, the role of water complexation in determining the lifetime of HO3•$\text{HO}_{3}^{\cdot}$ is incomplete without estimating the nonstatistical effect in HO₃··(H₂O) _n (n = 1 and 2) complexes. Therefore, in the present work, using direct dynamics simulations along with high-level electronic structure theory, the stability of these microsolvated systems is studied. The investigation suggests that the microsolvation of HO3•$\text{HO}_{3}^{\cdot}$ reduces its lifetime, and the non-RRKM effect is negligible as the system approaches the solution-phase.