Electron emission from ${\mathrm{CH}}_4$ molecules in collisions with fast bare C ions

We present the energy and angular distributions of electron emission from a ${\mathrm{CH}}_4$ molecule in collisions with fast bare C ions with energies 3.5 and 5.5 MeV/u. The absolute double differential cross sections (DDCS) are measured for the ejected electrons having energies from 11 eV to 330 eV for $3.5-\mathrm{MeV}/\mathrm{u}$ projectiles and from 5 eV to 330 eV for 5.5 MeV/u bare C ions. The emission is measured in the angular range from ${20}^{\circ }$ to ${160}^{\circ }$. The forward-backward angular asymmetry, the single differential cross sections (SDCS), and the total cross section are deduced from the measured DDCS values. The energy and angular distributions of the DDCS and SDCS are compared with those calculated using a theoretical model based on the prior form of the continuum distorted wave–eikonal initial state (CDW-EIS) approximation. The dynamics of the process is considered within the CDW-EIS approximation, while the initial orbitals of the molecular target are represented using the complete neglect of the differential overlap approximation. The calculations are found to be in very good agreement with the measured cross sections. The angle dependence of the carbon K-LL Auger emission and the total Auger emission cross section are also derived for both projectile energies.

Figure 1

Energy dependence of the ejected electron DDCS for ${\mathrm{CH}}_4$ in collisions with 5.5 MeV/u bare C ions. The K-LL Auger electron peaks are shown in the insets.

Figure 2

Same as in Fig. 1 but for 3.5 MeV/u bare C ion projectiles.

Figure 3

The angular distribution of DDCS of electron emission from the ${\mathrm{CH}}_4$ molecule in collisions with bare C ions. The observed and CDW-EIS values for 3.5 MeV/u projectiles are multiplied by a factor of 5.

Figure 4

Asymmetry parameter as a function of ejected electron velocity, $k$.

Figure 5

(a) Energy and (b) angle dependence of SDCS of electron emission. The measured and the CDW-EIS values for $3.5-\mathrm{MeV}/\mathrm{u}$ projectiles are multiplied by a factor of 5.

Figure 6

Angular dependence of carbon K-LL Auger emission cross section. The values for $3.5-\mathrm{MeV}/\mathrm{u}$ projectiles are multiplied by a factor of 2. Only relative errors are shown. Absolute errors are about 20%–25%.

Figure 7

The TCS as a function of ${\mathrm{C}}^{6+}$ projectile energy $E_P$.