Partitioning of excess energy in dissociative resonance capture processes

Abstract

The translational energies of selected negative ions formed by dissociative resonance capture processes from the polyatomic systems NF3, BF3, CF4, C2F6, C3F8, and c-C4F8 have been measured as functions of excess energy over the resonances. The excess energy in the molecular negative ion intermediate prior to dissociation has been calculated and partitioned into translational, vibrational, and, in some cases, electronic excitation of the dissociation products. The degree of vibrational activation in the intermediate state before dissociation is found to depend on the particular molecule under investigation and to vary from one dissociation channel to another. These observations are discussed in relation to theoretical concepts of dissociative resonance capture and given a qualitative explanation. The measurement of translational energy has led to a more complete interpretation of the states involved in the various processes and in computing ground state thermochemical properties of the decomposition products.

Cross Sections for Electron Collisions with NF3

“…These necessitated them to use a crossed beam geometry and an efficient solution to these problems was to use a segmented time-of-flight (TOF) mass spectrometer along with the pulsed-electron-beam and pulsed-ion-extraction techniques and the relative flow technique. The results of Harland and Franklin 19 and Nandi et al 20 agree well with each other in the positions of the resonance peaks, but the magnitude show the differences as nearly big as a factor of four. For example, the cross sections of the formation of F − are 0.…”

“…There are only two published reports, relevant to this evaluation purpose, on the absolute measurements of the dissociative electron attachment (DEA) cross sections for NF 3 : Harland and Franklin 19 and Nandi et al 20 Other than these, Chantry reported the DEA cross sections for NF 3 at a conference and the results were also contained in a book 21 but were not published in a journal, and therefore, this will not be discussed any further here. There are two experimental determinations of the electron attachment coefficient in swarms, 54,55 , but the two results are not consistent with each other and it is unclear which is more reliable.…”

“…In the following discussion, we neglect the hyper-fine interaction and mixing between singlet and triplet nuclear-spin states of NF 3 . The total wave function, including the nuclear-spin part, of NF 3 should be of the A 2 irreducible representation of the C 3v group because 19 F is a fermion. It means that for ortho-NF 3 , the space part (rovibronic) of the wave function should also be of the A 2 irreducible representation, because the nuclear spin part is totally symmetric, A 1 .…”

“…NF 3 is actually a greenhouse gas with a very high global warming potential which has led to concern on how it is used in the various technologies discussed above 13 . In spite of its importance, experimental studies of electron scattering on NF 3 are rather sparse: for total 14 and elastic 15 cross section measurements come from single laboratories, more measurements exist for ionization [16][17][18] and dissociative electron attachment [19][20][21] . In absence of experiments, several calculations [22][23][24][25] have been performed.…”

Crossed-beam experiment for the scattering of low- and intermediate-energy electrons from BF3: A comparative study with XF3 (X = C, N, and CH) molecules

“…ciative electron attachments, [6][7][8] grand total cross section (TCS) measured by Szmytkowski et al, 9 and calculated ionization and TCS with an independent atom model by Vinodkumar et al 10 Angular differential-vibrational excitation of BF 3 for symmetry stretching v 1 and degenerate stretching v 3 modes were reported as a function of the electron energy with a crossed-beam method by Tronc et al 11 As far as elastic differential cross sections (DCSs) and integral cross sections (ICSs) are concerned, we note a few theoretical studies on multi-scattering Xα-calculation of the unoccupied a ′′ 2 , a ′ 1 , and e ′ molecular orbitals of BF 3 and BCl 3 by Tossel et al 12 which are compared with electron transmission spectroscopy (ETS) measurements as well as R-matrix calculations by Radmilović-Radjenović 13 on the elastic scattering and electronic excitation of BF 3 by low energy electrons. More recently, the Schwinger multichannel (SMC) method was employed in the static-exchange (SE) and the static-exchange-polarization (SEP) approximations in the energy range from 0.1 to 10 eV.…”