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: CO 2, N 2 O, CH 4 - large molecules: - nitromethane - chlorobenzene - pyrrole - ethylene carbonate Threshold phenomena Electron collisions with a radical: NO ·

2

3

4 Sample Elastic Cross Sections

5

6 Differential cross sections in N 2 O Marinković B, Szmytkowski C, Pejčev V, Filipović D and Vuškoviš L, J. Phys. B (1986) Johnstone W M and Newell W R, J. Phys. B (1993) Kitajima M, Sakamoto Y, Gulley R J, Hoshino M, Gibson J C, Tanaka H and Buckman S J, J. Phys. B (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 CO 2 bending  = 0.0 D

13 N 2 O - Elastic & Vibrational Excitation elastic and fundamental vibrationsovertone vibrations  = 0.16 D

14 N 2 O - 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-d 4 : Role of Dipole-Bound Resonances M. Stepanović, Y. Pariat and M. Allan J. Chem. Phys. 110 (1999) 11376

16 Nitromethane CH 3 NO 2  = 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 NOfinal 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 O 2 NOO2O2

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?