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)].

Open-shell molecules in doubly degenerate 2E electronic states are subject to the E ⊗ e Jahn-Teller effect and spin-orbit interactions. The rotational structure of the ground vibrational level of the \documentclass[12pt]{minimal}\begin{document}$\tilde{\rm X}^+$\end{document}X̃+ 2E ground state of CH3F+ has been observed by high-resolution photoelectron spectroscopy. In contrast to what is observed in other members of the isoelectronic families \documentclass[12pt]{minimal}\begin{document}$\rm {CH}_3\rm {X}^+\,(\rm {X}=\rm {Cl,\,Br,\,I})$\end{document} CH 3X+(X= Cl , Br ,I) and \documentclass[12pt]{minimal}\begin{document}$\rm {CH}_3\rm {Y}\,(\rm {Y}=\rm {O,\,S})$\end{document} CH 3Y(Y=O,S), the spin-orbit interaction does not lead to a splitting of the ground state of CH3F+. Observed trends in the spectra of the \documentclass[12pt]{minimal}\begin{document}$\tilde{\rm X}$\end{document}X̃ 2E ground states of these molecules are summarized. Whereas certain trends, such as the reduction of the observable effects of the Jahn-Teller interactions and the increase of the spin-orbit splitting with increasing nuclear charge of X and Y are easily understood, other trends are more difficult to explain, such as the much reduced spin-orbit splitting in \documentclass[12pt]{minimal}\begin{document}$\rm {CH}_3\rm {F}^+$\end{document} CH 3F+ compared to \documentclass[12pt]{minimal}\begin{document}$\rm {CH}_3\rm {O}$\end{document} CH 3O. A simple two-state excitonic model is used to account for the trends observed within the series of the methyl-halide radical cations and also the similarities and differences between \documentclass[12pt]{minimal}\begin{document}$\rm {CH}_3\rm {F}^+$\end{document} CH 3F+ and the isoelectronic \documentclass[12pt]{minimal}\begin{document}$\rm {CH}_3\rm {O}$\end{document} CH 3O radical. Within this model, the electron hole in the 2E ground states of \documentclass[12pt]{minimal}\begin{document}$\rm {CH}_3\rm {X}^+$\end{document} CH 3X+ and \documentclass[12pt]{minimal}\begin{document}$\rm {CH}_3\rm {Y}$\end{document} CH 3Y is described in terms of contributions from the halogenic (or chalcogenic) px, y orbitals and the pyramidal-methylic (e) orbitals. This model enables a global, semi-quantitative description of the combined effects of the Jahn-Teller and spin-orbit interactions in these molecules and also a simple interpretation of the spin-orbit-coupling reduction factor ζe.

Laser initiated reactions in N2O clusters studied by time-sliced ion velocity imaging technique J. Chem. Phys. 139, 044307 (2013) We present a new photo-fragment imaging spectrometer, which employs a movable repeller in a single field imaging geometry. This innovation offers two principal advantages. First, the optimal fields for velocity mapping can easily be achieved even using a large molecular beam diameter (5 mm); the velocity resolution (better than 1%) is sufficient to easily resolve photo-electron recoil in (2 + 1) resonant enhanced multiphoton ionization of N 2 photoproducts from N 2 O or from molecular beam cooled N 2 . Second, rapid changes between spatial imaging, velocity mapping, and slice imaging are straightforward. We demonstrate this technique's utility in a re-investigation of the photodissociation of N 2 O. Using a hot nozzle, we observe slice images that strongly depend on nozzle temperature. Our data indicate that in our hot nozzle expansion, only pure bending vibrations -(0, v 2 , 0) -are populated, as vibrational excitation in pure stretching or bend-stretch combination modes are quenched via collisional near-resonant V-V energy transfer to the nearly degenerate bending states. We derive vibrationally state resolved absolute absorption cross-sections for (0, v 2 ≤ 7, 0). These results agree well with previous work at lower values of v 2 , both experimental and theoretical. The dissociation energy of N 2 O with respect to the O( 1 D) + N 2 1 + g asymptote was determined to be 3.65 ± 0.02 eV.

We present a 1 + 1' resonance-enhanced multiphoton ionization (REMPI) scheme for acetylene via the linear G̃ 4sσ (1)Πu Rydberg state, offering partial rotational resolution and the possibility to detect excitation in both the cis- and trans-bending modes. The resonant transition to the G̃ state is driven by a vacuum ultraviolet (VUV) photon, generated by resonant four-wave mixing (FWM) in krypton. Ionization from the short-lived G̃ state then occurs quickly, driven by the high intensity of the residual light from the FWM process. We have observed nine bands in the region between 79 200 cm(-1) and 80 500 cm(-1) in C2H2 and C2D2. We compare our results with published spectra in this region and suggest alternative assignments for some of the Renner-Teller split bands. Similar REMPI schemes should be applicable to other small molecules with picosecond lifetime Rydberg states.