LASER PHOTODETACHMENT SPECTROSCOPY OF THE S2- ION John Yukich Wade Morgan Andy Muhich Supported by Davidson College and the American Chemical Society

Negative Ion Formation + - - + - Electron attracted to neutral atom over ~ 1 atomic diameter Short-range interaction typically supports 1 or 2 bound states Electron correlation effects – partly responsible for covalent bonds Binding energy of extra electron is the electron affinity

Photodetachment - - - Neg. ion + photon → neutral atom + e- Similar to the photoelectric effect Occurs in earth’s ionosphere with sunlight !

Energy Levels of S2- → S2 S2 3∑-g S2- 2∏g V’ = 0 V” = 1 V” = 0 EA ≈ 13420 cm-1 (?) V” = 1 S2- 2∏g 570 cm-1 V” = 0

Optical Apparatus DPSS pump Ti:S ring laser Ion trap OCS leak 250 mW tunable ~750 nm Wavemeter (to 0.02 cm-1) Spectrum Analyzer 8 GHz FSR Ion trap OCS leak

S2- formation from OCS OCS + e- → S- + CO Dissociative attachment to carrier gas OCS Stumbled upon accidentally: OCS + e- → S- + CO S- + OCS → S2- + CO Confirmation of molecular species in trap: - dissociative electron energy - ion cyclotron resonance Pressure dependent

Ion cyclotron resonance for S2-

Δ = 1420 cm-1

Future work Analysis to determine electron affinity High-resolution spectroscopy Rotational constants Future ions: OD- , SH-, OH-

Trap electronics Lock-in amplifier To ADC

Photodetachment in 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 For typical B = 1.0 Tesla, ω ≈ 30 GHz, period = 36 ps Quantized Landau levels add structure to detachment cross section.