Rovibrationally Selected and Resolved Pulsed Field Ionization-Photoelectron Study of Ethylene

Abstract

We show that by preparing ethylene (C2H4) in selected rotational levels of the C−H stretching v 9(b2u) = 1 or v 11(b1u) = 1 state by infrared (IR) laser excitation prior to vacuum ultraviolet (VUV) laser photoionization, greatly simplified, rotationally resolved pulsed field ionization-photoelectron spectra can be obtained, leading to reliable rotational assignments of the vibrational bands for C2H4 +(X̃2B3u; v 4 +(torsional) = 1 or v 11 + = 1) ← C2H4(X̃Ag; v 11 = 1) and C2H4 +(X̃B3u; 00+) ← C2H4(X̃1Ag; v 9 = 1). The observation of these Franck−Condon (FC) forbidden vibrational bands is indicative of a strong state-mixing mechanism, in which Rydberg states converging to the FC forbidden C2H4 +(X̃2B3u; 00+ and v 4 + = 1) levels are effectively coupled via intermediate states to Rydberg levels converging to FC allowed C2H4 +(X̃2B3u; v 9 + = 1 and v 11 + = 1) states, respectively. This conclusion is supported by strong autoionizing features observed in the IR−VUV photionization efficiency spectra.

Rovibronic photoionization dynamics of asymmetric-top molecules

“…Resonant schemes rely on the existence of suitable intermediate states and offer the advantage of considerably reducing the rotational line density in the PFI-ZEKE photoelectron spectra by selecting a single rotational level in the first excitation step. The assignment of the spectra is thus facilitated and rotational resolution can often be achieved with light sources of moderate bandwidth such as pulsed dye lasers and synchrotrons, as has been demonstrated in recent studies using IR-VUV [40,92] and VUV-UV [93] (1 + 1 ) excitation sequences. Moreover, it is also possible to take advantage of the different Franck-Condon factors for the ionization from the intermediate state compared to the ionization from the ground neutral state, as has been shown in a recent PFI-ZEKE photoelectron spectroscopic study on thẽ X + 3 B 1 ground state of NH + 2 [94].…”

“…(3) for a given vibronic transition is their strict validity and their ease of implementation. They have successfully been applied to the analysis of the PFI-ZEKE photoelectron spectra of a number of polyatomic molecules such as ND 4 [75], NH 3 [76], C 6 H 6 [73,77], C 6 H 6 -rare gas clusters [78], H 2 O [73], CH 2 CO [37,38], CH 2 [32], NH 2 [33] and C 2 H 4 [39,40]. However, the drawback of these selection rules is that they provide only limited information on the photoionization dynamics (i.e., intensities) and primarily help to predict the even-or odd-nature of the photoelectron partial waves associated with a given rovibronic photoionization transition.…”

“…Partially resolved rotational contours have been analyzed in the photoelectron spectra of larger asymmetric tops such as, for instance, fluorobenzene [35] and n-butylbenzene [36]. The recent improvement of the resolution of PFI-ZEKE photoelectron spectroscopy to better than 0.1 cm −1 [19] enabled the observation of the rovibronic structure in the spectra of a wider range of asymmetric tops such as CH 2 CO [37,38], C 2 H 4 [39,40] and O 3 [41].…”

The Rotational Structure of the Origin Band of the Pulsed-Field-Ionization, Zero-Kinetic-Energy Photoelectron Spectra of Propene-h6 and Propene-d6

“…Thanks to the continual improvement of its resolution resulting from the exploitation of electric field ionization sequences, 15,24,25 PFI-ZEKE photoelectron spectroscopy, initially applied to resolve the rotational structure in the photoelectron spectra of diatomic molecules, has rapidly been applied to obtain information on the rovibrational photoionization of more com- ethene, 31,32 and allene. 33 The present results on propene illustrate the possibility of partially resolving the rotational structure in single-photon photoelectron spectra of structurally more complex molecules.…”

Torsional vibrational structure of the propene radical cation studied by high-resolution photoelectron spectroscopy

“…[25][26][27] The questions concerning the relative stability of the eclipsed and staggered conformations of cations containing CH 3 -CH=X functionalities can now be answered experimentally. For instance, Kim and his co-workers 28,29 have exploited mass-analyzed thresholdionization spectroscopy to study the methyl-torsional motion in CH 3 -CX=CH + 2 (X=Cl, Br) and found that the eclipsed form [ Fig.…”