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 - without dipole moment: CO 2 , N 2 O, CH 4 - large molecules: - nitromethane - chlorobenzene - pyrrole - ethylene carbonate Electron collisions with a radical: NO · 1

2

3

Sample Elastic Cross Sections 4

Sample Elastic Cross Sections 5

Differential cross sections in N 2 O 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) 6

Vibrational excitation in hydrogen fluoride: experiment and theory m = 1.83 D Martin Čížek, Jiří Horáček, Michael Allan and Wolfgang Domcke 2003 7

HF: Spectra and Potential Curves 8

HCl 9

HBr and DBr m = 0.82 D red: experiment blue: nonlocal resonance model Čížek Horáček Sergenton Popović Allan Domcke Leininger Gadea,

Phys. Rev

. A 2000 10

Generic potential curves 11

CO 2 m = 0.0 D bending 12

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

N 2 O - Dissociative Attachment Bound anion calculation: Kryachko

et al

., J. Chem. Phys. 2001 14

m = 5.3 D Ethylene Carbonate

Dissociative Electron Cyclopentanone, Attachment in

g

-Butyrolactone, Ethylene Carbonate and Ethylene Carbonate-d 4 : of Dipole-Bound Resonances Role

M. Stepanović, Y. Pariat and M. Allan J. Chem. Phys. 110 ( 1999 ) 11376 15

Nitromethane CH 3 NO 2 m = 3.46 D 16

Nitromethane: Elastic DCS 17

Selectivity of vibrational excitation in chlorobenzene m = 1.54 D 18

Pyrrole m = 1.77 D 19

Methane: Energy-Loss Spectrum 20

Methane: DCS overview W. Sohn, K.-H. Kochem, K.-M. Scheuerlein, K. Jung, H. Ehrhardt

J. Phys

. B

19

(1986) 3625 B. H. Lengsfield III, T. N. Rescigno, C. W. McCurdy,

Phys. Rev

. A

44

(1991) 4296 21

Methane: detail 22

Conclusions I Threshold phenomena - often interaction diffuse state ↔ valence state - diabatic

vs

adiabatic potential surfaces - vibrational Feshbach resonances (VFR) - outer well resonances - ( s * ) shape resonances - doorway states 23

24

Diffuse and Valence States of Anions 25

NO: Potential Curves initial NO NO – resonance final NO 26

NO: transitions between electronic fine structure states 27

NO: transitions between electronic fine structure states 28

NO: vibrational transitions 29

NO Comparison of NO and O 2 O 2 30

elastic NO: angular dependence Vibrational excitation 31

Conclusions II NO · : transitions between electronic fine structure states - gigantic resonant cross section,  elastic - resonance parentage - elastic cross sections not equal?

32