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+

Abstract

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)].

Time-resolved high-harmonic spectroscopy of the photodissociation of CH3I and CF3I

“…The cationic states were constructed using a Morse potential for a pseudodiatomic molecule. The X + states were modeled with the equilibrium distance Req = 2.126Å [41], the ground state vibrational wavenumberν 0 = 478.0 cm −1 [42], the dissociation energy De = 2.731 eV [43], the adiabatic ionisation energy Ip = 9.538 eV [44] to the X + 2 E 3/2 state and the spin-orbit splitting of 5050 cm −1 [45]. The parametersν 0 = 296.3 cm −1 , De = 0.925 eV, the zero point energy Te = 11.944 eV (all from [45]) and Req = 2.503Å [41] were used for the A + state.…”

The Jahn-Teller effect in ${\rm CH}_{\rm 3} {\rm Cl}^{\rm + } ( {{\rm \tilde X}{}^{\rm 2}{\rm E}} )$ CH 3 Cl +(X̃E2): A combined high-resolution experimental measurement and ab initio theoretical study

“…37 The bands at 32 (31) and 671 (665) cm −1 in the MATI spectra of CH 3 35 Cl (CH 3 37 Cl) are due to the rotational K-structure of CH 3 35 Cl + (CH 3 37 Cl + ). 23,25,26…”

“…Several photoelectron spectra studies for these molecules have been performed since 1970. [18][19][20][22][23][24][25][26] For CH 3 I + and a) Electronic mail: ymo@mail.tsinghua.edu.cn. b) Electronic mail: myungsoo@snu.ac.kr.…”

Photoelectron spectroscopic study of the E ⊗ e Jahn-Teller effect in the presence of a tunable spin-orbit interaction. III. Two-state excitonic model accounting for observed trends in the $\tilde{\rm X}^{\,2}{\rm {E}}$X̃2E ground state of $\rm {CH}_3\rm {X}^+\,(\rm {X}=\rm {F,\,Cl,\,Br,\,I})$ CH 3X+(X=F, Cl , Br ,I) and $\rm {CH}_3\rm {Y}\,(\rm {Y}=\rm {O,\,S})$ CH 3Y(Y=O,S)

“…The investigation of the photoelectron spectra of CH 3 I and CH 3 Cl at high resolution described in the first articles of this series, 15,16 together with the rotationally resolved photoelectron spectrum of the origin band of CH 3 F presented in Sec. II A of this article, provide additional information on the competition of the Jahn-Teller effect and spin-orbit coupling in these systems.…”

“…ζ e is referred to as the expectation value of L z ( ±| Lz |± = ±ζ e ) with respect to the two components (±) of the degenerate E state 22 and is sometimes thought of as arising from the off-axis atoms. 1,21 A distinctive advantage of our high-resolution pulsedfield-ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectroscopic studies of the Jahn-Teller effect in the cations CH 3 X + over the previous studies by He I PES is the possibility to determine the effective vibronic Coriolis coupling parameter ζ ev , 15,16 which in combination with the results from the vibronic analysis of the spectra of the X+ 2 E ground states [17][18][19] allows the determination of independent values for d j,v and ζ e .…”