Forward-to-backward differential-cross-section ratio in electron-impact vibrational excitation via the ${}^2\Pi$ resonance of CO

Electron-impact excitation of the CO molecule has been investigated by use of a crossed beam double trochoidal electron spectrometer. Forward and backward scattered electrons from the ${}^2\Pi$ resonance are analyzed. In order to separate these two contributions, electron beam modulation and time-of-flight detection of scattered electrons have been introduced. Backward electrons are additionally delayed in time by introduction of a decelerator device. The operation of this device is tested by a measurement performed on the ${}^2\Pi _g$ resonance in ${\mathrm{N}}_2$ molecule. The ratio of forward-to-backward scattered electrons from the ${}^2\Pi$ resonance in CO is found to be equal to 1, and thus the angular distribution of scattered electrons to be symmetric relative to 90°. This conclusion is compared to existing angular distribution measurements and theoretical predictions.

Figure 1

Experimental setup.

Figure 2

Time-of-flight spectrum of electrons scattered at 0° and 180° at incident energy at $1.91\mathrm{eV}$ from the $v=2$ level extitation in CO.

Figure 3

Angular distribution of electrons from ${}^2\Pi$ resonant extitation of CO at $1.91\mathrm{eV}$. Points at 0° and 180° are our data. Closed circles are data of Gibson et al. [11]. Open circles are data of Ehrhard et al. [4] and triangles of Tronc et al. [18]. The solid curve is the fit by Read’s theory [5] and the dashed curve Morgan’s [12] theory.