1. Breaking the Symmetry in Methyl Radical: High resolution IR spectroscopy of CH 2 D Melanie Roberts Department of Chemistry and Biochemistry, JILA University of Colorado at Boulder National Institute of Standards and Technology Chandra Savage, Feng Dong, David Nesbitt

2. Previous Work on CH 2 D M. E. Jacox, 1977  Matrix isolation spectroscopy J. L. Brum et al., 1993  Gas phase, REMPI  Electronic structure K. Kawaguchi, 2001  Gas phase, FTIR  Out-of-plane bending mode  Q, R branches only

3. The Broken Symmetry… CH 3 : 1 IR-active stretch  doubly-degenerate asymmetric stretch CH 2 D: 3 IR-active stretches  CH symmetric and CH antisymmetric stretch  CD stretch Hydrogen I= 1 / 2, Deuterium, I=1 CH 2 D: small dipole moment

4. Experimental Setup Servoloop locked optical transfer cavities for high frequency precision (~20 MHz)

5. Radical Source High radical densities at slit (~10 14 - 10 16 /cm 3 !) Sub-Doppler molecular linewidths (~40 MHz in Ne expansion) High radical densities at slit (~10 14 - 10 16 /cm 3 !) Sub-Doppler molecular linewidths (~40 MHz in Ne expansion)

6. Rotational Energy Levels 2 20 2 21 2 11 2 12 2 02 1 10 1 11 1 01 0 00 Energy labels: N KaKc Watson Hamiltonian C B A

7. Nuclear Spin Statistics Ψ=Ψ el Ψ vib Ψ rot Ψ ns --++α 1/√2 (α β +β α) β --+-1/√2(α β - β α) Electronic Vibration RotationNuclear Spin

8. Experimental Data

9. Symmetric Stretch: DFT calculations: B3LYP/6- 311++G(3df,3pd) Anharmonicity benchmarked to 10 CH radicals 1 10  2 11 1 01  2 02 1 10  2 11 0 00  1 01 1 11  1 10 1 10  1 11 2 11  2 12 1 01  0 00 2 12  1 11 2 02  1 01 2 11  1 10 3 13  2 12 3 03  2 02 3 12  2 11 Predictions Data

10. Boltzmann Plot Para Ortho T rot = 18.9(3) K

11. Ground State Rotational Constants AxisFTIR Studies * (cm -1 )This Work (cm -1 ) A 9.596969(89) 9.586(8 ) B 5.90686(49) 5.9067(1 ) C 3.6164(10) 3.6195(7 ) *K. Kawaguchi, 2001 Band Origin (cm -1 ) 3065.64(1)

12. What is really happening? CH bond length increases  Ground state: 1.0788(10)Å  Excited state: 1.0854(23)Å Rotational Constant changes (excited state – ground state)  ΔA = 0.16 cm -1  ΔB = 0.02 cm -1  ΔC = 0.03 cm -1

13. Fine and Hyperfine Terms Unsplit rotational level Spin- rotation splitting Nuclear hyperfine splitting J = N + S F 1 = J + I H 2 F 2 = F 1 +I D

14. Fine and Hyperfine Structure

15. Summary CH2D Symmetric Stretch Band  Rotational Structure  Fine Structure  Hyperfine Structure Antisymmetric Stretch Future Work Oxygenated Radicals

16. Acknowledgements Chandra Savage Feng Dong Scott Davis Erin Whitney David Nesbitt OSEP NSF/IGERT