recent experiments in low-energy electron-molecule collisions
DESCRIPTION
Recent Experiments in Low-Energy Electron-Molecule Collisions. Threshold phenomena. - valence s * shape resonances - diffuse dipole- (& polarizability-) bound resonances - vibrational Feshbach resonances - doorway states - molecules - with dipole moment: HF, HCl, HBr - PowerPoint PPT PresentationTRANSCRIPT
1
Recent Experiments in Low-Energy Electron-Molecule Collisions
- valence * shape resonances- diffuse dipole- (& polarizability-) bound resonances- vibrational Feshbach resonances- doorway states- molecules
- with dipole moment: HF, HCl, HBr- without dipole moment: CO2, N2O, CH4
- large molecules: - nitromethane- chlorobenzene- pyrrole- ethylene carbonate
Threshold phenomena
Electron collisions with a radical: NO·
2
3
4
Sample Elastic Cross Sections
5
Sample Elastic Cross Sections
6
Differential cross sections in N2O
Marinković B, Szmytkowski C, Pejčev V, Filipović D and Vuškoviš L,J. Phys. B 19 2365 (1986)
Johnstone W M and Newell W R, J. Phys. B 26 129 (1993)
Kitajima M, Sakamoto Y, Gulley R J, Hoshino M, Gibson J C, Tanaka H and Buckman S J, J. Phys. B 33 1687 (2000)
7
Vibrational excitation in hydrogen fluoride: experiment and theory
Martin Čížek, Jiří Horáček, Michael Allan and Wolfgang Domcke 2003
= 1.83 D
8
HF: Spectra and Potential Curves
9
HCl
10
Čížek Horáček Sergenton Popović Allan Domcke Leininger Gadea, Phys. Rev. A 2000
HBr and DBr red: experiment
blue: nonlocal resonance model = 0.82 D
11
Generic potential curves
12
CO2
bending
= 0.0 D
13
N2O - Elastic & Vibrational Excitation
elastic and fundamental vibrations overtone vibrations
= 0.16 D
14
N2O - Dissociative Attachment
Bound anion calculation: Kryachko et al., J. Chem. Phys. 2001
15
Ethylene Carbonate = 5.3 D
Dissociative Electron Attachment in Cyclopentanone, -Butyrolactone, Ethylene Carbonate and Ethylene Carbonate-d4: Role of Dipole-Bound ResonancesM. Stepanović, Y. Pariat and M. AllanJ. Chem. Phys. 110 (1999) 11376
16
Nitromethane CH3NO2
= 3.46 D
17
Nitromethane: Elastic DCS
18
Selectivity of vibrational excitation in chlorobenzene
= 1.54 D
19
Pyrrole
= 1.77 D
20
Methane: Energy-Loss Spectrum
21
Methane: DCS overview
B. H. Lengsfield III, T. N. Rescigno, C. W. McCurdy, Phys. Rev. A 44 (1991) 4296
W. Sohn, K.-H. Kochem, K.-M. Scheuerlein, K. Jung, H. Ehrhardt J. Phys. B 19 (1986) 3625
22
Methane: detail
23
Conclusions I
- often interaction diffuse state ↔ valence state
- diabatic vs adiabatic potential surfaces
- vibrational Feshbach resonances (VFR)
- outer well resonances
- (*) shape resonances
- doorway states
Threshold phenomena
24
25
Diffuse and Valence States of Anions
26
NO: Potential Curves
initial NO final NONO– resonance
27
NO: transitions between electronic fine structure states
28
NO: transitions between electronic fine structure states
29
NO: vibrational transitions
30
Comparison of NO and O2
NO O2
31
NO: angular dependence
elastic Vibrational excitation
32
Conclusions II
NO·: transitions between electronic fine structure states
- gigantic resonant cross section, elastic
- resonance parentage
- elastic cross sections not equal?