June 18, nd Symp. on Molec. Spectrosc. Activation of C-H Bonds: Pure Rotational Spectroscopy of HZnCH 3 ( 1 A 1 ) M. A. Flory A. J. Apponi and L. M. Ziurys University of Arizona Department of Chemistry Department of Astronomy Steward Observatory

June 18, nd Symp. on Molec. Spectrosc. Metal Activation of C-H Bonds One of MAIN themes in modern chemistry Variety of applications –Petroleum industry (hydrocarbon refining) –Catalysis (homogeneous and heterogeneous) –Inorganic synthesis (oxidative addition) C-H bond is strong kcal/mol ( cm -1 ) Many transition metals insert into CH 4 upon photoexcitation to produce ‘methylmetal hydrides’ in matrices –M + CH 4 → HMCH 3 → ·CH 3 + MH No gas-phase isolation or observation of HMCH 3 –Theoretical calculations on reaction pathways –Matrix IR studies of bending modes

June 18, nd Symp. on Molec. Spectrosc. Instrument designed for identifying molecular ions Additional application for synthesizing neutrals from organometallic precursors - Longitudinal AC discharge - New chemical regime Gunn oscillators/Schottky diode multipliers ( GHz) Double walled, glass cell with 2 ring electrodes Detector: InSb bolometer Radiation is modulated at 25kHz and detected at 2f Direct Absorption Spectroscopy with an AC Discharge

June 18, nd Symp. on Molec. Spectrosc. Searching for ZnCH 3 ( 2 A 1 ) Not in Broida or Ion cell Zn(CH 3 ) 2 – 2 mTorr 250 W AC discharge Scanned > 30 GHz Repeating SINGLET Slightly lower B than ZnCH 3 CH 4 and H 2 improved signal Concluded that molecule is HZnCH 3 ( 1 A 1 ) –Highly unexpected! 7 isotopologues observed –H 64 ZnCH 3, H 66 ZnCH 3, H 67 ZnCH 3, H 68 ZnCH 3 –D 66 ZnCH 3, D 68 ZnCH 3 –H 64 Zn 13 CH 3 Spectral Search

June 18, nd Symp. on Molec. Spectrosc. Attempting Zn(CH 3 ) 2 in FTMW J = 1-0, K = 18 GHz J = 2-1, K = 36 GHz Synthesis Conditions –0.2 % Zn(CH 3 ) 2 in Ar –No laser ablation needed –No H 2 or CH 4 –1000 V, 50 mA DC discharge –Pulsed at 10 Hz Search for rare isotopes in high S:N – 67 Zn eqQ –Closed shell molecule –Nature of bonding Fourier Transform Spectroscopy

June 18, nd Symp. on Molec. Spectrosc. HZnCH 3 and Hyperfine Interactions H 67 ZnCH 3 (X 1 A 1 ) J K ;F=2 0 ;4.5→1 0 ; ;2.5→1 1 ; ;3.5→1 0 ; ;4.5→1 1 ; ;0.5→1 0 ;1.5 Portion of the 67 Zn (4%) quadrupole splitting K = 0 and 1 intermixed Also observed I. J interaction of methyl H in main isotopologue J = 1  0 K = 0 F = 2.5  1.5 F = 1.5  1.5 F = 0.5  1.5 H 64 ZnCH 3 (X 1 A 1 )

June 18, nd Symp. on Molec. Spectrosc. Analysis and Structure (MHz)H 64 ZnCH 3 J  J′K obs-calc Data fit using a symmetric top Hamiltonian Up to K = 7 in 12 rotational transitions Relatively large eqQ indicates covalent bonding - eqQ ( 67 ZnF) = -60 MHz Geometry of HZnCH 3 and Similar Molecules (1  errors) HZnCH 3 ZnCH 3 ZnHHZnCl r0r0 rsrs rere r0r0 r0r0 r0r0 r HZn (Å) (4)1.521(4) (4) r ZnC (Å) (6)1.928(4) (7) r CH (Å)1.140(3)  H-C-H (deg) (9) (MHz)H 64 ZnCH 3 H 67 ZnCH 3 B (74) (39) DJDJ (61) (13) D JK (45) (27) H JK (27) H KJ (65) C I (H 3 ) (13) C I ( 67 Zn) (53) eqQ( 67 Zn) (11) rms Linear H-Zn-C backbone H-Zn and Zn-CH 3 bond lengths shorter than in fragment species H-Zn bond similar to HZnCl Spectroscopic Constants Sample Transition Frequencies

June 18, nd Symp. on Molec. Spectrosc. Gas Phase Metal Insertion to CH 4 Zn(CH 3 ) 2 + AC Zn + CH 4 + DC HZnCH 3 is believed to be a reaction intermediate of: Zn + CH 4  HZnCH 3  ZnH +. CH 3 Repeated experiment –Zn (vapor) + CH 4 + DC –Broida oven Spectrum was reproduced!! Evidence that excited Zn atoms may insert into C-H bonds DO see 1 A 1 state in gas phase –Contrary to predictions that ground state only accessible in matrix * *

June 18, nd Symp. on Molec. Spectrosc. Expanding utility for Ziurys group ion and FTMW spectrometers Increasing synthesis options –AC discharge –Not Broida-oven limited –New organometallic precursors –New classes of molecules Determined structure of HZnCH 3 Established H 67 ZnCH 3 electric quadrupole constant – Covalent bonding Have shown evidence for direct gas phase insertion of Zn into CH 4 through 1 A 1 state Conclusions 1.521(4) Å 1.928(4) Å 1.140(3) Å 110.2(3)° Zn C

June 18, nd Symp. on Molec. Spectrosc. Acknowledgements Lucy Ziurys Ziurys Group –Dr. Aldo Apponi –Dr. DeWayne Halfen –Stefanie Milam, Robin Pulliam, Ming Sun, Emmy Tenenbaum Funding –NSF –NASA Laboratory Astrophysics