Development of the Hamiltonian and matrix elements for partially deuterated methoxy radical

112

The B̃-X̃ laser-induced-fluorescence spectrum of jet-cooled isopropoxy radical (i-C3H7O[middle dot]) has been recorded. Using an isolated state model the observed rotational and fine structure of the origin band has been well simulated to determine rotational constants for both the X̃ and B̃ states and the electron spin-rotation constants of the X̃ state. The line intensities are well simulated with a parallel transition type, requiring the same symmetry for the levels involved of each the X̃ and B̃ state, which confirms the previous suggestion that going from ethoxy (C2H5O[middle dot]) to isopropoxy, the energy ordering of the electron configurations with in- and out-of-plane half-filled p-orbitals of the oxygen atom is reversed and the ground vibronic symmetry changes from a" to a'. However, the observed spin-rotation coupling constants are not consistent with their predication from either semi-empirical theory or quantum chemical calculations. Additionally, the lack of observed transitions involving the out-of-plane transition moment component is not consistent with high level electronic structure calculations suggesting mixing of vibronic levels by strong spin-orbit coupling. A new twofold model has been developed that explicitly includes Coriolis and spin-orbit coupling between different vibronic levels. This model renders the discrepancy between theoretical and experimental spin-rotation constants moot. Moreover, it determines independently the contributions to the observed splitting between the lowest two levels, resulting from non-relativistic kinetic and Coulombic effects, and that due to the relativistic spin-orbit interaction. The experimental values show that these effects are comparable, but that the vibronic one is slightly more important. This result is at variance with state-of-the-art electronic structure calculations which otherwise do a remarkably good job of describing the ground state of isopropoxy.

Section: Transition Intensitiesmentioning

confidence: 99%

Rotationally resolved ${\tilde{B}} \leftarrow {\tilde{X}}$B̃←X̃ electronic spectra of the isopropoxy radical: A comparative study

Liu

Melnik

Miller

2013

112

“…26 Despite these studies, the rovibronic structures of the methyl-halide cations remain less well characterized and understood than is the case for the corresponding isoelectronic neutral molecules CH 3 O and CH 3 S, for which high-resolution spectra have been obtained and analyzed. 3,[27][28][29][30] The methoxy radical, in particular, has served as a prototypical molecule to study the Jahn-Teller effect and spin-orbit coupling, and represents one of the best understood molecular systems subject to the E ⊗ e Jahn-Teller effect (see Refs. 3, 27, 29, and 30 and references therein).…”

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)].

“…For the convenience of treatment of the spin-orbit and spinrotational interaction and their effects on the rotational level structure, the ERH is referenced to an internal axis system (IAS) (Ref. 25) in which the z-axis is parallel to the C-O bond and the unique hydrogen nucleus is placed in xz-plane. To obtain physically meaningful parameters of the asymmetrically substituted species, the analysis is performed consistently with that of the symmetrically substituted species 20,21 and provides the appropriate isotopic relationships between the spectral parameters.…”

Section: A Groundx 2 E Electronic Statementioning

confidence: 99%

“…It is evident that capturing the effects of Jahn-Teller distortion in a molecule with lowered nuclear symmetry requires developing a detailed model that describes the spectra in terms of quantities with clearly defined physical meaning, connected to the molecule's geometric and electronic properties. We previously developed such a model and showed 25 that the symmetry lowering results in a more complex effective rotational Hamiltonian than that for the symmetrically substituted radicals. Herein, we extend our previous 21,[25][26][27] development of the effective rotational and spin-rotational Hamiltonian to elucidate the physical interpretation of the first, X 1 , and the second, X 2 , order contributions to the effective molecular parameters.…”

Section: Introductionmentioning

confidence: 99%

“…We previously developed such a model and showed 25 that the symmetry lowering results in a more complex effective rotational Hamiltonian than that for the symmetrically substituted radicals. Herein, we extend our previous 21,[25][26][27] development of the effective rotational and spin-rotational Hamiltonian to elucidate the physical interpretation of the first, X 1 , and the second, X 2 , order contributions to the effective molecular parameters. We also obtain isotopic relationships for the parameters of the effective rotational Hamiltonian which enable comparison of results from asymmetrically deuterated species with those of normal 20 and perdeuterated 21 isotopologues.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The spectroscopic characterization of the methoxy radical. III. Rotationally resolved $\skew3\tilde{A}^2A_1\text{–}\skew3\tilde{X}^2E$Ã2A1–X̃2E electronic and $\skew3\tilde{X}^2E$X̃2E submillimeter wave spectra of partially deuterated CH2DO and CHD2O radicals

Melnik

Liu

Chen

et al. 2011

Rotationally resolved laser induced fluorescence and stimulated emission pumping Ã(2)A(1)-X̃(2)E spectra, along with pure rotational spectra in the 153-263 GHz region within the E(3/2) component of the ground state in asymmetrically deuterated methoxy radicals CH(2)DO and CHD(2)O have been observed. The combined data set allows for the direct measurement with high precision of the energy separation between the E(1/2) and E(3/2) components of the ground state and the energy separation between the parity stacks in the E(3/2) component of the ground state. The experimentally observed frequencies in both isotopologues are fit to an effective rotational Hamiltonian accounting for rotational and spin-rotational effects arising in a near-prolate asymmetric top molecule with dynamic Jahn-Teller distortion. Isotopic dependencies for the molecular parameters have been successfully implemented to aid the analysis of these very complex spectra. The analysis of the first and second order contributions to the effective values of molecular parameters has been extended to elucidate the physical significance of resulting molecular parameters. Comparisons of measured parameters, e.g., spin-orbit coupling, rotational and spin-rotation constants, are made among the 5 methoxy isotopologues for which data is now available. Comparisons of experimental results, including the derived geometric structure at both the C(3v) conical intersection and at the Jahn-Teller distorted minima, are made with quantum chemistry calculations.