Rotationally Resolved State-to-State Photoelectron Study of Molybdenum Monoxide Cation (MoO+)

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• 作者：Zhihong Luo ; Yih-Chung Chang ; Yi Pan ; Kai-Chung Lau ; C. Y. Ng
• 刊名：Journal of Physical Chemistry A
• 出版年：2016
• 出版时间：July 14, 2016
• 年：2016
• 卷：120
• 期：27
• 页码：4643-4654
• 全文大小：621K
• 年卷期：0
• ISSN：1520-5215

文摘

By employing the two-color visible–ultraviolet (vis–UV) laser pulsed field ionization–photoelectron (PFI–PE) measurement, we have obtained rotationally selected and resolved photoelectron spectra for the MoO⁺(X⁴Σ^–; v⁺ = 0, 1, and 2) and MoO⁺(a²Δ_3/2,5/2; v⁺ = 0 and 1) cationic states. The unambiguous rotational assignments have made possible the determination of highly precise values for the band origin v₀₀⁺ = 60 147.9 ± 0.8 cm^–1, rotation constant B₀⁺ = 0.4546 ± 0.0006 cm^–1, spin–spin coupling constant λ = 26.454 ± 0.017 cm^–1, and bond length r_e⁺ = 1.642 ± 0.001 Å for the MoO⁺(X⁴Σ^–) ground state; v₀₀⁺ = 60 556.4 ± 0.8 cm^–1, B₀⁺ = 0.4711 ± 0.0005 cm^–1, and r₀⁺ = 1.613 ± 0.001 Å for the MoO⁺ (a²Δ_3/2) excited state; and v₀₀⁺ = 61 718.2 ± 0.8 cm^–1, B₀⁺ = 0.4695 ± 0.0006 cm^–1, and r₀⁺ = 1.616 ± 0.001 Å for the MoO⁺ (a²Δ_5/2) excited state. The ionization energy (IE) for MoO is determined to be IE(MoO) = 60 095.1 ± 0.8 cm^–1 [7.4508 ± 0.0001 eV]. Furthermore, the vibrational constants are determined as ω_e⁺ = 1000 ± 9 cm^–1 and ω_e⁺x_e⁺ = 5 ± 3 cm^–1 for MoO⁺(X⁴Σ^–); the vibration spacing ΔG(1/2) for MoO⁺(a²Δ_3/2) is also measured as 1065 ± 4 cm^–1. On the basis of the thermochemical cycle, together with the known IE(Mo) and the IE(MoO) determined in this study, the difference of 0 K bond dissociation energy for MoO⁺ and that for MoO is determined to be D₀(Mo⁺–O) – D₀(Mo–O) = IE(Mo) – IE(MoO) = −2890.8 ± 0.9 cm^–1 [−0.3584 ± 0.0001 eV]. The energetic and spectroscopic values determined here have been used for benchmarking calculations at the CCSDTQ/CBS level of theory. The CCSDTQ/CBS predictions, IE(MoO) = 7.457 eV, r_e⁺ = 1.651 Å, ω_e⁺ = 974 cm^–1, D₀(Mo–O) = 5.386, and D₀(Mo⁺–O) = 5.015 eV, are found to be in good agreement with the vis–UV PFI–PE measurements. We also recommend a set of equally reliable CCSDTQ/CBS thermochemical values for MoO and MoO⁺: ΔH°_f0(MoO) = 383.7, ΔH°_f298(MoO) = 384.0, ΔH°_f0(MoO⁺) = 1103.2, and ΔH°_f298(MoO⁺) = 1103.5 kJ mol^–1.