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 ~~

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

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 ~ ~~ ~

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 ~~ ~~

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

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 ~~ ~

High Resolution Spectra CaCH 3 and SrCH 3

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

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

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

ParameterX2A1X2A1 B2A1B2A1 T (64) A5.393 a (84) B (24) (14) DNDN (16) x D NK (77) x (1.8) x  aa (21) (  bb +  cc )/ (51) x (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)

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

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

CaCH 3 B 2 A 1 Perturbation ~

~ F 2 Levels Pushed Down

CaCH 3 B 2 A 1 Perturbation ~

Results and Analysis CaCH 3 ParameterX2A1X2A1 B2A1B2A1 T (60) A a B (25) (98) DNDN (29) x D NK (32) x  aa (  bb +  cc )/ (41) x (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

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 )/ ~  E B-A ~~

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) r C-H (Å) a  H-C-H (º) b a Structure a) Fixed to DFT Calculations (Chan and Hamilton 1998) b) Fixed to Ground State Value ~~~~ ~ ~

Future Work and Acknowledgements Funding: NSERC