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LASER SPECTROSCOPY AND DYNAMICS OF THE JET-COOLED AsH2 FREE RADICAL

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Presentation on theme: "LASER SPECTROSCOPY AND DYNAMICS OF THE JET-COOLED AsH2 FREE RADICAL"— Presentation transcript:

1 LASER SPECTROSCOPY AND DYNAMICS OF THE JET-COOLED AsH2 FREE RADICAL
Sheng-Gui He & Dennis J. Clouthier Department of Chemistry University of Kentucky Lexington, KY AND MORE…

2 AsH2 : A GaAs CVD Intermediate
HEAT Atoms on a GaAs surface visualized by scanning tunneling microscopy

3 Background AsH2 high resolution electronic spectrum studied by flash photolysis (Dixon, 1968) AsH2 emission observed in 193 nm photolysis of AsH3 (Kong, 1986) Microwave studies of AsH2 and AsD2 (Saito, 1998) Very complete set of ground state constants from far-IR LMR (Evenson, 2000) No LIF or emission spectra of jet-cooled AsH2

4 Pulsed Discharge Jet Apparatus AsH3 & Argon

5 AsH2 0−0 Band

6 AsH2 0−0 Band Spin & Hyperfine Structure

7 SRL Emission Spectrum 110(F2) 220 000

8 Molecular Structures ~ …(9a1)1 (4b1)2 A 2A1 4b1 (HOMO) ~
…(9a1)2 (4b1)1 X 2B1 9a1 (SHOMO)

9 AsH2 Parameters “Pure precession” εaa = 4Aζ4p 9a1 = 10.5% As 4s ΔE
Parameter (cm-1) Ground State Excited State ω10 2096.5(9) 2112.7(1) ω20 984.4(6) 852.2(2) εaa [-1.11] 4.718 [4.28] aF(As) 0.0512(14) “Pure precession” εaa = 4Aζ4p 9a1 = 10.5% As 4s ΔE 4b1 (HOMO) 9a1 (SHOMO)

10 Fluorescence Lifetimes

11 Predissociation Process
AsH2 As (4Su) + H2 (1Sg+) As (4Su) + 2H AsH (X 3S-) + H ~ X 2B1 a 4A2 A 2A1 J. Chem. Phys. 126, (2007)

12 A New Spectrum

13 Simulation of High-Resolution Spectrum

14 H2AsO: A New Free Radical

15 Ground State Vibrations
n2 sym. AsH bend Expt: 948 cm-1 Calc: 974 cm-1 n3 As-O stretch Expt: 841 cm-1 Calc: 841 cm-1 n4 AsH wag Expt: 518 cm-1 Calc: 541 cm-1 Calc. = B3LYP/aug-cc-pvtz

16 H2AsO Electronic States
~ T0 = cm-1 B2A' …(π)1 (n)2 (π*)2 ~ T0 = 5400 cm-1 A2A" …(π)2 (n)1 (π*)2 (Ab initio) ~ T0 = 0.0 cm-1 X 2A' …(π)2 (n)2 (π*)1

17 Comparisons of H2XO Radicals
Phosphoryl radicals: nonplanar, reactive, polymer chem. Nitrosyl radicals: planar, spin trap, R2NO stable Arsenyl radicals: nonplanar, reactive?

18 LIF spectrum of jet-cooled AsH2 observed.
AsH2 molecular structures determined. Excited state fluorescence lifetimes measured. Predissociation mechanism proposed. Identification of the spectrum of the AsH2O free radical.

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