The Ramsauer minimum of methane

Ramsauer-Townsend minimum in methane — modified effective range analysis

“…To choose recommended vibrational integral CS we performed a thorough screening of theories [15,45,51,52], beam experiments [30,31] and swarm analysis [29,49,50]. We found that present MERT-derived integral elastic CS (σ IE ) combined with the theoretical vibrational CS (σ 2,4 + σ 1,3 ) by Althorpe et al [45] reproduced almost perfectly up to 1 eV the absolute total CS obtained in several alternative-type experiments and extended to low energies [35][36][37]47]. Such a combination not only provides a quantitative agreement, but also, most of all, it reconstructs the detailed shape of the experimental data.…”

“…Ferch et al [35] used four parameters to model their total cross sections below 0.5 eV of impact energy; Schmidt [29] in his analysis including the d-wave shift used six parameters (see Ref. [29] for detailed explanations).…”

“…(3) swarm-derived [29] momentum transfer cross sections and (4) grand total cross sections [35][36][37]. As a starting point for comparisons we used elastic differential cross sections (DCS) at selected energies [17] and swarm-derived momentum transfer cross sections [29], but those data alone did not allow us to obtain a mutual consistency.…”

“…(1) Experimental total cross sections were measured from 0.085 eV by Ferch et al [35], from 0.1 V by Lohmann and Buckman [36] and from 1.3 eV by Jones [37]; their data are shown in Figure 3. Measurements by Zecca et al [47], coinciding within the error bar with those of Jones, are given only at a few energy points and with only two-digit precision, so they do not introduce any new information and they are not shown in Figure 3.…”

“…Therefore, in the present analysis, the elastic cross sections in CH 4 are completed with experimental and theoretical data on vibrational excitation and compared with absolute measurements of total cross sections [35][36][37]. The Boltzmann two-term model [38] is used additionally to check the consistency of elastic and vibrational cross sections with experimental electron-drift coefficients.…”