Rovibrational-state-selected pulsed field ionization-photoelectron study of methyl iodide using two-color infrared-vacuum ultraviolet lasers

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Two-color visible-ultraviolet (VIS-UV) resonance-enhanced laser photoionization and pulsed field ionization-photoelectron (PFI-PE) study of gaseous titanium monoxide (TiO) in the total energy range of 55,000-57,320 cm(-1) has been conducted. The TiO molecules were selectively excited to single J' rotational levels of the intermediate TiO*(B(3)Π1, ν' = 0) state by using a VIS dye laser and then ionized by using another UV laser. This two-color photoexcitation method has allowed the measurement of cleanly J(+)-resolved PFI-PE spectra for the TiO(+)(X (2)Δ(5/2,3/2); v(+) = 0, 1, and 2) vibrational bands. By simulating the rotationally resolved PFI-PE spectra, J(+) = 3∕2 is determined to be the lowest rotational level of the ground electronic state, confirming that the symmetry of the TiO(+) ground state is (2)Δ(3/2). Irregular intensity patterns for rotational PFI-PE peaks that deviated from the regular patterns that favor the rotational transitions with small change of the core rotational angular momentum, are observed. This observation is indicative of strong perturbations of the PFI-PE rotational transitions, possibly by a channel-coupling mechanism. The analysis of the PFI-PE spectra yields highly precise values for the adiabatic ionization energy of TiO [IE(TiO) = 55 005.4 ± 0.8 cm(-1) (6.81980 ± 0.00010 eV)], and the vibrational frequency (ωe(+) = 1056.1 ± 0.8 cm(-1)), the anharmonicity constant (ωe(+)χe(+) = 4.4 ± 0.8 cm(-1)), the rotational constants (B(e)(+) = 0.5613 ± 0.0009 cm(-1) and αe(+) = 0.0029 ± 0.0008 cm(-1)), and the equilibrium bond length (r(e)(+) = 1.583 Å) for the TiO(+)(X (2)Δ(3/2)) ground state, the vibrational frequency (ωe(+) = 1058.4 ± 0.8 cm(-1)), the anharmonicity constant (ωe(+)χe(+) = 5.1 ± 0.8 cm(-1)), the rotational constants (B(e)(+) = 0.5715 ± 0.0007 cm(-1) and αe(+) = 0.0030 ± 0.0004 cm(-1)) and the equilibrium bond length (r(e)(+) = 1.568 Å) for the excited spin orbit state TiO(+)(X (2)Δ(5/2)), along with the spin-orbit coupling constant (A = 105.9 ± 0.2 cm(-1)) for TiO(+)(X (2)Δ(5/2,3/2)).

Section: Resultssupporting

confidence: 91%

Section: Resultsmentioning

confidence: 99%

Rovibronically selected and resolved two-color laser photoionization and photoelectron study of titanium monoxide cation

Huang

Luo

Chang

et al. 2013

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“…This observation is consistent with the N + changes observed in the state-to-state photoionization studies of CH 3 I, CH 3 Br, FeC, and NiC. 10,11,[23][24][25] Due to the interference of the background electron peaks, the maximum N + change observed in the PFI-PE spectra of Figs. 4(a)-4(d) for the CoC + (X 1 + ; v + = 0) is limited to 3 or 4 and the lowest rotational level identified is N + = 2 from N = 6.…”

Section: Resultssupporting

confidence: 90%

Rovibronically selected and resolved two-color laser photoionization and photoelectron study of cobalt carbide cation

Huang

Chang

Luo

et al. 2013

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We have conducted a two-color visible-ultraviolet (VIS-UV) resonance-enhanced laser photoionization efficiency and pulsed field ionization-photoelectron (PFI-PE) study of gaseous cobalt carbide (CoC) near its ionization onset in the total energy range of 61,200-64,510 cm(-1). The cold gaseous CoC sample was prepared by a laser ablation supersonically cooled beam source. By exciting CoC molecules thus generated to single N' rotational levels of the intermediate CoC∗((2)Σ(+); v') state using a VIS dye laser prior to UV laser photoionization, we have obtained N(+) rotationally resolved PFI-PE spectra for the CoC(+)(X(1)Σ(+); v(+) = 0 and 1) ion vibrational bands free from interference by impurity species except Co atoms produced in the ablation source. The rotationally selected and resolved PFI-PE spectra have made possible unambiguous rotational assignments, yielding accurate values for the adiabatic ionization energy of CoC(X(2)Σ(+)), IE(CoC) = 62,384.3 ± 0.6 cm(-1) (7.73467 ± 0.00007 eV), the vibrational frequency ωe (+) = 985.6 ± 0.6 cm(-1), the anharmonicity constant ωe (+)χe (+) = 6.3 ± 0.6 cm(-1), the rotational constants (Be (+) = 0.7196 ± 0.0005 cm(-1), αe (+) = 0.0056 ± 0.0008 cm(-1)), and the equilibrium bond length re (+) = 1.534 Å for CoC(+)(X(1)Σ(+)). The observation of the N(+) = 0 level in the PFI-PE measurement indicates that the CoC(+) ground state is of (1)Σ(+) symmetry. Large ΔN(+) = N(+) - N' changes up to 6 are observed for the photoionization transitions CoC(+)(X(1)Σ(+); v(+) = 0-2; N(+)) ← CoC∗((2)Σ(+); v'; N' = 6, 7, 8, and 9). The highly precise energetic and spectroscopic data obtained in the present study have served as a benchmark for testing theoretical predictions based on state-of-the-art ab initio quantum calculations at the CCSDTQ∕CBS level of theory as presented in the companion article.

“…Theoretical studies of the Jahn-Teller effect have been reported that account for the vibronic structure observed in these He I photoelectron spectra. [12][13][14] Mass-analyzed thresholdionization (MATI) and pulsed-field-ionization zero-kineticenergy (PFI-ZEKE) photoelectron spectra of theX + ←X transitions of CH 3 I, its fully deuterated isotopomer CD 3 I, and CH 3 Br with partial resolution of the rotational structure have also been recorded and analyzed, [15][16][17][18][19][20] providing insights into the complex interplay of vibronic, spin-orbit, and rotational effects in Jahn-Teller-coupled systems.…”

Section: Introductionmentioning

confidence: 99%

Photoelectron spectroscopic study of the E⊗e Jahn–Teller effect in the presence of a tunable spin–orbit interaction. I. Photoionization dynamics of methyl iodide and rotational fine structure of CH3I+ and CD3I+

Grütter

Michaud

Merkt

2011

The high-resolution single-photon pulsed-field-ionization zero-kinetic-energy photoelectron spectra of the \documentclass[12pt]{minimal}\begin{document}$\tilde{\rm {X}}^+$\end{document}X̃+ 2\documentclass[12pt]{minimal}\begin{document}$\rm {E_{3/2}}\leftarrow \tilde{\rm {X}}\, ^1{\rm A}_1$\end{document}E3/2←X̃1A1 transition of CH3I and CD3I have been recorded. The spectral resolution of better than 0.15 cm−1 enabled the observation of the rotational structure. CH3I+ and CD3I+ are subject to a weak \documentclass[12pt]{minimal}\begin{document}$\rm {E}\otimes \rm {e}$\end{document}E⊗e Jahn–Teller effect and strong spin–orbit coupling. The treatment of the rovibronic structure of the photoelectron spectra in the corresponding spin double group, \documentclass[12pt]{minimal}\begin{document}$\rm {C_{3v}^2(M)}$\end{document}C3v2(M), including the effects of the spin–orbit interaction and the vibrational angular momentum, allowed the reproduction of the experimentally observed transitions with spectroscopic accuracy. The relevant spin–orbit and linear Jahn–Teller coupling parameters of the \documentclass[12pt]{minimal}\begin{document}$\tilde{\rm {X}}^+$\end{document}X̃+ ground state were derived from the analysis of the spectra of the two isotopomers, and improved values were obtained for the adiabatic ionization energies [\documentclass[12pt]{minimal}\begin{document}${E_{\rm {I}}(\rm {CH}_3\rm {I})}/hc =76931.35(20)$\end{document}EI( CH 3I)/hc=76931.35(20) cm−1 and \documentclass[12pt]{minimal}\begin{document}${E_{\rm {I}}(\rm {CD}_3\rm {I})}/hc=76957.40(20)$\end{document}EI( CD 3I)/hc=76957.40(20) cm−1] and the rotational constants of the cations. Rovibronic photoionization selection rules were derived for transitions connecting neutral states following Hund's-case-(b)-type angular momentum coupling and ionic states following Hund's-case-(a)-type coupling. The selection rules, expressed in terms of the angular momentum projection quantum number P, account for all observed transitions and provide an explanation for the nonobservation of several rotational sub-bands in the mass-analyzed threshold-ionization spectra of \documentclass[12pt]{minimal}\begin{document}$\rm {CH}_3\rm {I}$\end{document} CH 3I and \documentclass[12pt]{minimal}\begin{document}$\rm {CD}_3\rm {I}$\end{document} CD 3I reported recently by Lee et al. [J. Chem. Phys. 128, 044310 (2008)].