First-principles simulations of transition state spectra of the I + HI and I + DI reactions and vibrational bonding in IMuI

Highlights: • Ab initio low-lying potential energy surfaces for the I + HI reaction. • Transition-state spectra of the I + HI and I + DI reactions are simulated. • Ground-state potential energy surface supports I-Mu-I vibrational bonding state. - Abstract: The lowest three potential energy surfaces for the I(²P_3/2, ²P_1/2) + HI(X¹Σ) reaction have been developed using extensive ab initio electronic structure calculations including the spin–orbit interaction. Using the ab initio potential energy surfaces, we simulate experimentally-observed transition state spectra for the I + HI and I + DI reactions by calculating photodetachment spectra of the IHI⁻ and IDI⁻ anions. Very good agreement was obtained between theory and experiment. When the hydrogen atom is replaced by Mu, which is a very light isotope of hydrogen, it was found that the I + MuI reaction system has a bound vibrational-bonding state whose wavefunction is highly localized around the transition state region on the ground-state potential energy surface. All other systems containing heavier hydrogen isotopes show only a van der Waals bonding feature