photodetachment spectroscopy from cooled negative ions
DESCRIPTION
Photodetachment spectroscopy from cooled negative ions. Summer research in the AMO lab* June – August 2005. James Wells. * Support from Davidson College and the American Chemical Society. -. -. -. -. -. +. +. -. -. -. -. Photodetachment. -. X - + photon → X + e - - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Photodetachment spectroscopy from cooled negative ions](https://reader035.vdocuments.net/reader035/viewer/2022062305/568167a9550346895ddcf661/html5/thumbnails/1.jpg)
Photodetachment Photodetachment spectroscopy from cooled spectroscopy from cooled
negative ionsnegative ions
James WellsJames Wells
Summer research in the AMO lab*June – August 2005
* Support from Davidson College and the American Chemical Society
![Page 2: Photodetachment spectroscopy from cooled negative ions](https://reader035.vdocuments.net/reader035/viewer/2022062305/568167a9550346895ddcf661/html5/thumbnails/2.jpg)
PhotodetachmentPhotodetachment
--
- -
-+
- -
- -
+ -
• X- + photon → X + e-
• Equivalent to latter half of an electron-atom collision.
![Page 3: Photodetachment spectroscopy from cooled negative ions](https://reader035.vdocuments.net/reader035/viewer/2022062305/568167a9550346895ddcf661/html5/thumbnails/3.jpg)
Effects of ions’ random motionEffects of ions’ random motion
Photon frequency is Doppler Photon frequency is Doppler broadenedbroadened Causes uncertainty Causes uncertainty ΔΔE in any energy-E in any energy-
dependent measurementdependent measurement Typical experimental goal: measure Typical experimental goal: measure
probability of detachment as f(Eprobability of detachment as f(Ephotonphoton)) ΔΔE blurs experimental results: fewer E blurs experimental results: fewer
details, less contrast/structure.details, less contrast/structure.
![Page 4: Photodetachment spectroscopy from cooled negative ions](https://reader035.vdocuments.net/reader035/viewer/2022062305/568167a9550346895ddcf661/html5/thumbnails/4.jpg)
Evaporative coolingEvaporative cooling
Ions trapped in an ion trap: electrostatic Ions trapped in an ion trap: electrostatic potential well.potential well.
Cooling appletCooling applet
![Page 5: Photodetachment spectroscopy from cooled negative ions](https://reader035.vdocuments.net/reader035/viewer/2022062305/568167a9550346895ddcf661/html5/thumbnails/5.jpg)
Ion trap apparatusIon trap apparatus
![Page 6: Photodetachment spectroscopy from cooled negative ions](https://reader035.vdocuments.net/reader035/viewer/2022062305/568167a9550346895ddcf661/html5/thumbnails/6.jpg)
Ring dye laserRing dye laser
![Page 7: Photodetachment spectroscopy from cooled negative ions](https://reader035.vdocuments.net/reader035/viewer/2022062305/568167a9550346895ddcf661/html5/thumbnails/7.jpg)
Laser LabVIEW control codeLaser LabVIEW control code
(Screen shot)
![Page 8: Photodetachment spectroscopy from cooled negative ions](https://reader035.vdocuments.net/reader035/viewer/2022062305/568167a9550346895ddcf661/html5/thumbnails/8.jpg)
![Page 9: Photodetachment spectroscopy from cooled negative ions](https://reader035.vdocuments.net/reader035/viewer/2022062305/568167a9550346895ddcf661/html5/thumbnails/9.jpg)
Negative Ion FormationNegative Ion Formation
• Short-range attractive potential (~ 2 eV deep and a few Å wide)
• Electron correlation effects – partly responsible for covalent bonds
- +--
- -
--
- -
-+
![Page 10: Photodetachment spectroscopy from cooled negative ions](https://reader035.vdocuments.net/reader035/viewer/2022062305/568167a9550346895ddcf661/html5/thumbnails/10.jpg)
Energy Levels (Oxygen)Energy Levels (Oxygen)
![Page 11: Photodetachment spectroscopy from cooled negative ions](https://reader035.vdocuments.net/reader035/viewer/2022062305/568167a9550346895ddcf661/html5/thumbnails/11.jpg)
Photodetachment with B-FieldsPhotodetachment with B-Fields• departing electron executes cyclotron motion in field
• motion in plane perpendicular to B is quantized to cyclotron levels
• cyclotron states separated by ω = eB/me
• motion along axis of field is continuous, non-quantized
• for typical B = 1.0 Tesla, ω ≈ 30 GHz, period = 36 ps
• quantized Landau levels add structure to detachment cross section
![Page 12: Photodetachment spectroscopy from cooled negative ions](https://reader035.vdocuments.net/reader035/viewer/2022062305/568167a9550346895ddcf661/html5/thumbnails/12.jpg)
Trap electronicsTrap electronics
![Page 13: Photodetachment spectroscopy from cooled negative ions](https://reader035.vdocuments.net/reader035/viewer/2022062305/568167a9550346895ddcf661/html5/thumbnails/13.jpg)
Detachment cross section in B Detachment cross section in B fieldfield