State-to-state predissociation dynamics of hydroxyl radical via the A²Σ⁺ state

ABSTRACT

Photo-predissociation dynamics of jet-cooled hydroxyl radical (OH) via several rovibrational levels (v′ = 2–4, N′ = 0–2, J′ = 0.5–2.5, F₁) in the A²Σ⁺ state are studied using the high–n Rydberg-atom time-of-flight (HRTOF) technique. Spin–orbit branching fractions and angular distributions of the H(²S) + O(³P_{J = 2,1,0}) product channels are measured in the product translational energy distributions. The A²Σ⁺ v′ = 2 and 3 states of OH predissociate predominantly via the single 1⁴Σ⁻ repulsive state, while the A²Σ⁺ v′ = 4 state predissociates via the 1⁴Σ⁻, 1²Σ⁻, and 1⁴Π repulsive states and quantum interferences among these dissociation pathways play an important role in the O(³P_{J = 2,1,0}) product fine-structure state distribution. The experimental O(³P_J) product spin–orbit branching ratios are in excellent agreement with the full quantum multichannel scattering calculations that include all the interactions in the crossing region, recoupling zone, and asymptotic zone [Parlant and Yarkony, J. Chem. Phys. 110, 363 (1999)]. The product angular distributions strongly depend on the rotational transitions and rotational levels in the A²Σ⁺ state. The measured anisotropy parameters are in reasonable agreement with predictions from the simulation programme (Betaofnu) [Kim et al., J. Chem. Phys. 125, 133316 (2006)], using dissociation lifetime, excitation frequency, rotational level, and rotational constant. The predissociation time scales of OH A²Σ⁺ are determined to be 130 ± 30 ns and ≥ 14 ± 3 ps for the v′ = 2, N′ = 2, J′ = 2.5 and v′ = 4, N′ = 0, J′ = 0.5 levels, respectively.

GRAPHICAL ABSTRACT

KEYWORDS:

• Photodissociation
• hydroxyl radical
• spectroscopy
• predissociation

Acknowledgement

This work was supported by the US National Science Foundation (grant number CHE-1566636) and partially by a UC MEXUS-CONACYT Collaborative Grant (CN-16-68).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the US National Science Foundation (grant number CHE-1566636) and partially by a UC MEXUS-CONACYT Collaborative Grant (CN-16-68).