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

- 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.

The lowest three potential energy surfaces for the I(2P3/2, 2P1/2) + 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.

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