Photoionization spectra of CH3I perturbed by SF6: electron scattering in SF6 gas

Abstract

A photoionization study of CH 3 I in the presence of SF 6 perturbers (up to the perturber density 9.75 x 10 19 cm -3 ) disclosed a red shift of autoionizing features that depends linearly on the perturber number density. From the perturber induced energy shifts of the CH 3 I nd! Rydbergs (n=9,10,11,12), the electron scattering length of SF 6 was found to be A = -0.484 nm, which accords with previously reported (but less precise) cross section data. An assessment is made of the validity of the impact approximation used in the data analysis presented here. 2(1)

Photoionization spectra of CH3I and C2H5I perturbed by CF4andc-C4F8: electron scattering in halocarbon gases

“…Photoionization and photoabsorption spectra were measured with monochromatic synchrotron radiation (with a resolution of 0.09 nm, or ∼8 meV in the spectral region of interest) [20], which entered a copper experimental cell [17,21] equipped with entrance and exit MgF 2 windows. This cell, which is capable of withstanding pressures of up to 100 bar, possesses two parallel plate electrodes (stainless steel, 3 mm spacing) aligned perpendicular to the windows, thus allowing for the simultaneous measurement of photoionization and transmission spectra.…”

“…CH 3 I (Aldrich Chemical, 99.5%), C 2 H 5 I (Sigma, 99%), CF 4 (Matheson Gas Products, 99.999%) and c-C 4 F 8 (Matheson Gas Products, 99.98%) were used without further purification. Both the gas handling system and the procedures employed to ensure homogeneous mixing of the dopant and perturber have been described previously [17,22,23]. The dopant pressures measured in the gas handling system were reproducible to within ±0.01 mbar, and the perturber pressures were reproducible to within ±0.1 bar for the high number density range [22].…”

“…An alternative method for determining the zero-kinetic-energy electron scattering cross section of a gas involves perturber-induced energy shifts of high-n Rydberg states [13][14][15][16][17][18][19] of a dopant molecule. In this method, a dopant molecule having a Rydberg series observable in photoabsorption and/or photoionization spectroscopy is mixed with a perturber gas of interest.…”

“…The perturber-induced energy shifts of high-n Rydberg states have been used to obtain the zero-kinetic-energy electron scattering lengths of numerous gases [16,17], including the electronegative gases CO 2 [18] and SF 6 [17,19].…”

Field ionization and photoionization of CH3I perturbed by diatomic molecules: electron scattering in H2, HD, D2and O2

“…An alternative to the direct measurement of scattering cross-sections involves determining A from the fluid densityinduced energy shifts (ρ) of high-n Rydberg states [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] of a dopant molecule. In this approach, a dopant possessing a Rydberg series observable in photoabsorption and/or photoionization is mixed with the fluid of interest.…”