69th International Symposium on Molecular Spectroscopy, Champaign-Urbana, Illinois June 16-20, 2014
Vibrational Spectroscopy of Transient Dipolar Radicals via
Autodetachment of Dipole-Bound States of Cold Anions
Speaker: Dao-Ling Huang
Research advisor: Prof. Lai-Sheng Wang
Co-workers: Dr. Hong-Tao Liu
Phuong Diem Dau
Department of Chemistry, Brown University
Dipole-Bound State (DBS)
• Theoretical prediction: Electrons can be weakly bounded if point dipole moment >1.6 D.
• Experimental Observation:
Real molecules can form “dipole bound” anions if dipole moment > 2.5 D.
For example:
H2O, NH3 are stable molecules.
H2O─, NH3 ─ do not exist.
(H2O)2 ─ , (H2O…NH3)- , (H2O)N ─ , (NH3)M ─ exist.
•
1.
2.
3.
Typical techniques to study DBS:
Rydberg state transfer
Electron resonance photodetachment
Photoelectron spectroscopy (PES)
Typical DBS, (H2O)4−
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K. R. Lykke, D. M. Neumark, T. Andersen, V. J. Trapa, W. C. Lineberger, Phys. Rev. Lett. 52, 2221 (1984)
Nathan I. Hammer, Joong-Won Shin, Jeffrey M. Headrick, Eric G. Diken, Joseph R. Roscioli, Gary H. Weddle, Mark A. Johnson , Science 306,
675 (2004)
The Current Apparatus
the Constant Kinetic Energy Peak at Room Temperature (RT)
Daniel M. Neumark et al., Phys. Chem. Chem. Phys.
13, 17378- 17383 (2011)
Preliminary Understanding of Vibrational
Autodetachment of DBS
Cooling anion to very low temperature is important to better understand the observation.
5
Non-Resonant PE Spectra of Phenoxide
RT
20 K
H. T. Liu, C. G. Ning, D. L. Huang, P. D. Dau, and L. S. Wang, Angew. Chem. Int. Ed. 125, 9146-9149 (2013)
Relative Electron Counts
Excitation Spectrum to the v11 Vibrational Levels
of the DBS of Phenoxide
519 cm-1
519 cm-1
H. T. Liu, C. G. Ning, D. L. Huang, P. D. Dau, and L. S. Wang, Angew. Chem. Int. Ed. 125, 9146-9149 (2013)
Energy Level Diagrams for the
DBS, Propensity Rule ∆ = -1
H. T. Liu, C. G. Ning, D. L. Huang, P. D. Dau, and L. S. Wang, Angew. Chem. Int. Ed. 125, 9146-9149 (2013)
Dehydrogenated Uracil Anion
[Uracil-H]−
Uracil
- H+
+
Vibrational Spectroscopy of the Dehydrogenated Uracil Radical
Via Autodetachment of Dipole-Bound Excited States of Cold Dehydrogenated Uracil anions
H. T. Liu, C. G. Ning, D. L. Huang, and L. S. Wang, Angew. Chem. Int. Ed. 53, 2464-2468 (2014)
Assignment of Fundamental Vibrational Levels
mode
symmetry
theoretical
v1
A’
3581
experimental
peak
v2
3222
v3
3145
v4
1713
1705
42
v5
1694
1672
41
v6
1469
1451
33
v7
1437
v8
1411
v9
1342
1316
31
v10
1301
1285
30
v11
1186
1154
26
v12
1082
1057
22
v13
982
970
20
v14
920
910
18
v15
757
753
13
v16
583
577
8
v17
545
540
7
v18
501
492
6
v19
392
389
5
v20
A”
980
v21
803
804
15
v22
734
727
12
v23
684
666
10
v24
633
615
9
v25
357
360
4
v26
152
150
v27
113
113
H. T. Liu, C. G. Ning, D. L. Huang, and L. S. Wang, Angew. Chem. Int. Ed. 53, 2464-2468 (2014)
Summary
• The second-generation cold ion trap coupled with high-resolution photoelectron
imaging is a powerful experimental set-up to probe DBS of anions.
• Vibrational spectroscopy of dipolar radicals can be obtained via autodetachment
of DBS of anions.
Acknowledgement
C.G. Ning