1. HIGH RESOLUTION SPECTROSCOPY OF THE B 2 A 1 - X 2 A 1 TRANSITION OF CaCH 3 and SrCH 3 P. M. SHERIDAN, M. J. DICK, J. G. WANG AND P. F. BERNATH University of Waterloo ~~

2. Metal Polyatomic Molecules MCH 3, MCCH, MSH, MNH 2 … –Interest in Catalysis, Organic Synthesis, Biological Systems, Astrochemistry… Not As Well Characterized As Diatomic Counterparts Lower Symmetry Complicates Spectra –Simplify Analysis by Characterizing these Species in a Molecular Jet/Laser Ablation Source –See TC08, TC09, and TC10

3. First Gas Phase Observation (Brazier and Bernath 1987) –Low Resolution Spectra: Ca and Sr Reacting w/Methyl Precursors CaCH 3 A 2 E – X 2 A 1 (Brazier and Bernath 1989) –High Resolution Spectrum in Broida Oven MgCH 3 A 2 E – X 2 A 1 (Rubino, Williamson and Miller 1995) –High Resolution Jet Cooled Spectrum Alkaline - Earth Monomethyls ~ ~~ ~

4. Optical Stark Spectra CaCH 3 (Marr et al 1996) –Determined Dipole Moments in A 2 E and X 2 A 1 States Millimeter-Wave Spectroscopy (Ziurys Group) –Ground State Pure Rotational Spectra of Mg, Ca, Sr, and BaCH 3 Low-Lying States Not all Well Characterized at High Resolution –Initiated a Study of the B-X Transitions of CaCH 3 and SrCH 3 Using Molecular Jet/Laser Ablation Techniques Alkaline - Earth Monomethyls ~~ ~~

5. Boxcar Delay Box Pulsed Valve Power Supply Scope YAG 3 rd Harmonic Rod Rotator Single Mode Ring Dye Laser Pump Gas In (1% Sn(CH 3 ) 4 in Ar) Backing Pressure (100 psi) I 2 Cell w/ PMT PC PMT Preamp Laser Ablation Source T rot ~ 4–8 K

6. B 2 A 1 – X 2 A 1 Transition CaCH 3 and SrCH 3 –Prolate Symmetric Top –C 3v Symmetry B 2 A 1 Correlates to B 2  –|| type transitions –a-dipole moment –  K = 0 Nuclear Spin Statistics –Rotationally Cool into Both K" = 0 and 1 Levels ~~ ~

7. High Resolution Spectra CaCH 3 and SrCH 3

8. Energy Level Diagram K = 0 Sub-Band Resembles Hund’s Case(b) 2  – Case(b) 2  Transition 4 Main Branches 2 Satellite Branches Branch Notation  N  J Fi'Fi" F 1 : J = N + S; F 2 : J = N – S

9. Energy Level Diagram K = 1 Sub-Band Resembles Hund’s Case(b) 2  – Case(b) 2  Transition 6 Main Branches 6 Satellite Branches

10. SrCH 3 B 2 A 1 – X 2 A 1 K = 0 and 1 Sub-Bands ~~

11. ParameterX2A1X2A1 B2A1B2A1 T0.014787.58135(64) A5.393 a 5.31139(84) B0.193833336(24)0.193603(14) DNDN 2.14893(16) x 10 -7 0.0 D NK 1.61313(77) x 10 -5 5.4(1.8) x 10 -5  aa 0.0-0.2523(21) (  bb +  cc )/2 4.12162(51) x 10 -3 -0.14879(11) Results and Analysis SrCH 3 Data Fit to Symmetric Top Hamiltonian –108 B 2 A 1 – X 2 A 1 Transitions and Pure Rotational Transitions –Fit Using Pickett’s Program ~ ~~ ~ a) Fixed to Theoretical Value (Chan and Hamilton 1998)

12. CaCH 3 B 2 A 1 – X 2 A 1 K = 0 Sub-Band ~~ Q Branch K = 1?

13. CaCH 3 B 2 A 1 – X 2 A 1 K = 1 Sub-Band ~~

14. CaCH 3 B 2 A 1 Perturbation ~

15. ~ F 2 Levels Pushed Down

16. CaCH 3 B 2 A 1 Perturbation ~

17. Results and Analysis CaCH 3 ParameterX2A1X2A1 B2A1B2A1 T0.016010.19538(60) A5.44831 a B0.252384881(25)0.2532525(98) DNDN 3.54514(29) x 10 -7 D NK 1.99593(32) x 10 -5  aa (  bb +  cc )/2 1.47842(41) x 10 -3 -0.03604(12) K = 0 Sub Band Fit to Symmetric Top Hamiltonian –58 K = 0 B 2 A 1 – X 2 A 1 Transitions and Pure Rotational Transitions Calculated Term Values for K' = 1 Levels ~~ ~~ a) Fixed to Optical Value

18. Spin Rotation Constants – Assume Unpaired Electron in a p Orbital – Unique Perturber Assumption –Relatively Good Agreement with Pure Precession Approximation Pure Precession in CaCH 3 and SrCH 3 B 2 A 1 (  bb +  cc )/2 = – 2l(l+1)BA so CaCH 3 SrCH 3 cm -1 MeasuredCalculatedMeasuredCalculated (  bb +  cc )/2 -0.03604-0.053-0.14879-0.209 ~  E B-A ~~

19. Rotational Constants Fit to C 3v Moment of Inertia Equations –CaCH 3 B State Structure Not Reliable –SrCH 3 B State M-C Bond Slight Increase: H-C-H Angle Opens CaCH 3 SrCH 3 StateX2A1X2A1 B2A1B2A1 X2A1X2A1 B2A1B2A1 r M-C (Å)2.3482.1552.4872.492 r C-H (Å) a 1.102 1.104  H-C-H (º) 105.3105.3 b 105.8 a 107.0 Structure a) Fixed to DFT Calculations (Chan and Hamilton 1998) b) Fixed to Ground State Value ~~~~ ~ ~

20. Future Work and Acknowledgements Funding: NSERC