Excitation transfer from He(235,21,S) into bound and continuum states of CS2 studied by electron and optical spectroscopy and by coincidence measurements

Abstract

For the reaction of He(23S, 21S) with CS2 we present a large body of experimental data: electron spectra, fluorescence spectra, electron-ion and electron-photon coincidence spectra. The combination of all these data allows us to characterize the reaction in great detail in a way which is rather direct and free of speculations. As for other molecules with positive electron affinity the charge exchanged channel He + + CS~ plays an important role as intermediate state. It is possible to isolate experimentally the electron energy spectra which correspond to formation of the individual electronic CS2 + states out of the intermediate He + +CS2 state. This has not been achieved so far for CS2 or any other molecule by straightforward evaluation of experimental data. L IntroductionThe reaction of metastable helium He(23S) and CS2 has been investigated before by means of electron spectroscopy [1,2] and in flowing afterglow by optical spectroscopy [3,4]. However, the existence of a second entrance channel He + +CS2-in addition to the covalent entrance channel He*+CSz has so far escaped attention even though it is responsible for the major part of all reactions. Since CS2 has a positive electron affinity of EA =0.54 eV [5] the importance of the configuration He + +CS~ is not surprising in view of the behaviour of other molecules with positive electron affinity like NO2, SO2, 02 and C12 [64].In this paper we present for the reaction of He(23S) and CS2 the improved electron energy spectrum and -measured in the same machine under the same conditions -the fluorescence spectrum from 1,800-8,800A. The same set of data was obtained for the first time for the other metastable species He(21S). For comparison we have in addition taken these data for impact of 584 A (HeI) photons. Further, for the system He(23S)+CS2, we have carried out two types of coincidence measurements. We have taken spectra of electrons which are coincident * Dedicated to Prof. O. Osberghaus on the occasion of his 65th birthday with either of the parent or fragment ions. On the other hand we have measured the spectrum of electrons which are emitted in coincidence with CSf(/? -J() emission around 284 nm. The paper is organized as follows: in Sect. II we describe briefly our experimental setup and in Sect. III we present our measured data and point out similarities and discrepancies to existing literature. In the following section we undertake the attempt to develop a picture of the He(23S, 21S)+C82 reactions which incorporates all experimentally observed features.

Resonant spectra of quadrupolar anions

“…Moreover, the g.s. of CS − 2 is bent [93,94,98,101] with an angle of about 132 ○ . The predicted linear excited state of CS − 2 thus appears as a "doorway state" to the g.s.…”

Reactions of metastable argon with photodissociation aligned carbon disulfide: A study of the steric dependence of two competing reaction channels

“…Secondly, Penning ionization electron spectroscopy studies on the ionization ofCS 2 by He (2 IS) and He (2 3S) show the existence in those cases of long-range curve crossings to ionic intermediate potentials. 31 The location of such crossings depends on the reactive electron affinity of CS 2 ,32,33 the ionization potential of the metastable, and the orientation along the collision trajectory. Since the ionization potentials of the Ar* 3P2 and 3P O states 34 lie between those of the He* IS and 3 S states, the ionic potentials are also expected to be important in the reactions of Ar* with CS 2 .…”

Electron spectroscopy of liquid mercury under impact of metastable He(23S) atoms

“…[13] contains a detailed description of the liquid target whereas the metastable atom beam source and the electron spectrometer are described in previous publications [14,15]. Only a short description follows here.…”