HIGHRESOLUTION LASERINDUCED FLUORESCENCE LIF SPECTROSCOPY OF THE DEUTERATED

HIGH-RESOLUTION LASER-INDUCED FLUORESCENCE (LIF) SPECTROSCOPY OF THE DEUTERATED ISOTOPOMERS OF THE METHOXY RADICAL JINJUN LIU, JOHN T. YI AND TERRY A. MILLER Laser Spectroscopy Facility Department of Chemistry The Ohio State University 06/20/06

Outline Talk I q q (TJ 04): Motivation and goals Experiment q q CH 3 O, control and example q q q Experimental apparatus Calibration method Error analysis and experimental accuracy Simulation and fitting Prediction of microwave transitions Summary Talk II q (TJ 05): CH 2 DO and CHD 2 O q q q q Experiment Effective Hamiltonian Transition intensities CD 3 O Global fitting (LIF and microwave) Summary and future work Acknowledgment

Motivation q q Alkoxy radicals (RO·) are key components in the oxidation of hydrocarbons both in combustion and in the atmosphere. 3 cm -1 simplest alkoxy radical is an interesting Energy/10 Methoxy (CH 3 O), the molecule for dynamic studies. ~ CH 3 O CH 2 O+H 3 CH 3+O( P) CH 3 O(A 2 A 1) Methoxy has also very important theoretical interest due to its Jahn-Teller 30 effect, coupled to spin-orbit interaction. The partial deuteration of the methoxy radical (CHD 2 O & CH 2 DO). q q 20 the molecular symmetry. Breaks Removes the degeneracy in the electronic ground state. Turns 10 Jahn-Teller effect to pseudo-Jahn-Teller effect. H 2 CO+H Introduces new terms into the rovibronic Hamiltonian of CH 3 O. HCO+H 2 bands. • Extra vibrational • Different rotational structures. 0 CH 2 OH ~ CH 3 O(X 2 E) General hydrocarbon oxidation scheme in the atmosphere. * J. A. J. Geers, Orlando, G. S. Tyndall, Temps, T. L. J. and Wallington, J. W. Wiebrecht, Rev. J. Chem. 103, 4657 Phys. (2003) 101, 117, 3618(1994) Han, Y. J. G. Kappert, Utkin, H. F. Chen, A. Burns, and. Chem. R. F. Curl, J. Chem. Phys. 6538 (2002).

Chronicle 1984 Endo et al, microwave spectrum of CH 3 O. 1988 Foster et al, moderateresolution 1990 LIF of CH 3 O. Liu et al, high-resolution LIF ~ of CH 3 O (A state spin-rotation splittings only). Microwave LIF 2001, Kalinovski, lowresolution LIF of CH 2 DO and CHD 2 O 2004 Melnik et al, microwave spectrum of CH 2 DO and CHD 2 O 2006, Liu et al, high-resolution LIF of CH 3 O, CH 2 DO, CHD 2 O and CD 3 O, and global fitting with mw.

Experimental Apparatus PMT Doubling Crystal Xe. F Photolysis Laser ~5 -10 m. J Pulse Amplifier Vacuum Chamber Box. Car CHx. D 3 -x. ONO +first-run Ne ~0. 5 m. J Etalon (75% Ne+25%He) Ar+ Laser 20 W PD ~100 m. W Chopper (2 KHz) T~3 K Computer Calibration System Excimer Laser (Xe. Cl) I 2 CW Ring Dye Laser 1 -3 m. W Lockin PD 50 cm λ/2 Plate PBS a. H. Kato et. al. , “Doppler-Free High Resolution Spectral Atlas of Iodine Molecule”, Japan Society of the Promotion of Science, (2002) (Experimental) b. B. Bodermann, H. Knöckel, E. Tiemann, Iodine. Spec 4 (2002) (Computational)

LIF Spectrum of CH 3 O John-Teller active mode. Allowed ~ due to 2 E symmetry of the X state and the Jahn-Teller distortion. * S. C. Foster, X. P. Misra, T. D. Lin, C. P. Damo, C. C. Carter, and T. A. Miller, J. Phys. Chem. 92, 5914 (1988)

Rotationally Resolved LIF Spectrum of Moderate-resolution* (FWHM~6 GHz) High-resolution (FWHM~300 MHz) * D. E. Powers, M. B. Pushkarsky, and T. A. Miller, J. Chem. Phys. 106, 6863 (1997) Band

a b Frequency/cm-1 a. Broader than the other three isotopomers (~250 MHz). b. B. Bodermann, H. Knöckel, E. Tiemann, Iodine. Spec 4, Toptica Photonics, Munich, Germany, (2002)

Error Analysis and Calibration Method q q q Computational iodine Atlas (σ~1. 5 MHz) Density of iodine lines (~1/(10 GHz), i. e. separation~20 FSRs) Instability of FSR of the etalon (σ~0. 05 MHz) Mechanical instability (~-1. 5 KHz/μm) q Drift of the index of refraction of the air (thermal: ~0. 5 KHz/ o. C, flow…) q Thermal expansion of the Invar frame of the etalon (~-0. 1 KHz/ o. C) q Incident angle q Nonlinearity of cw ring laser (~1%, <2. 5 MHz(=1/2× 500 MHz× 1%)) q q Uncertainty of picking up the peaks q q q LIF peaks (~50 MHz, dominant) Iodine peaks (~1. 5 MHz) Etalon fringes (~1. 5 MHz) q Frequency chirping of the pulsed dye amplifier (~10 MHz, affects only q Iodine peaks for absolute calibration Etalon fringes for relative calibration Whole spectrum calibrated using cubic spline interpolation q q T 00)* * I. Reinhard, M. Gabrysch, B. F. Weikersthal, K. Jungmann, and G. Putlitz, Appl. Phys. B. , 63, 476 (1996)

Experimental Accuracy and Proof q Based on the propagation of all experimental errors, an estimation of accuracy σ~50 MHz q Calibration of iodine peaks comparing with atlas (σ<10 MHz) Reproducibility of different calibrated scans (σ<50 MHz) q q q σ depends on the frequency separation between the calibrated peaks to the closest iodine peaks and/or etalon fringes Prediction of microwave transitions based on combination differences of LIF spectra a. Corrected for hyperfine splittings. b. Y. Endo, S. Saito, and E. Hirota, J. Chem. Phys. 81, 122, (1984)

CH 3 O, 320 Band Experimental Simulation

q q q 73 transitions HEFF = HROT + HCOR + HSO + HSR 11 Constants Ground state (2 e, Hund’s case a) A”, B”, Aζt”, aζed”, ε q Excited state (2 a, Hund’s case a) A’, B’, εaa’, εbc’ q Te q M_|_: M||=1: 0 q T=3 K q Standard deviation = 41 MHz q aa”, εbc” Spin-rotation interaction Spin-orbit interaction Coriolis interaction Rotational

CH 3 O, 610 Band Experimental q q 90 transitions 13 Constants Ground state (2 e, Hund’s case a): A”, B”, Aζt”, aζed”, ε aa”, εbc” q Excited state (2 e, Hund’s case a): A’, B’, Aζt’, εaa’, εbc’, ε 1’ q Te q q q Simulation M_|_: M||=1: 2 Standard deviation = 74 MHz

Molecular Constants

Prediction of Microwave Transitions a. Corrected for hyperfine splittings. b. Y. Endo, S. Saito, and E. Hirota, J. Chem. Phys. 81, 122, (1984)

Summary and Future Work (TJ 05) q q q Hi-resolution LIF apparatus improved by the new calibration system (σ~50 MHz). Hi-resolution LIF spectra of CH 3 O ( and bands). Successful simulation and fitting. Ground electronic state constants from the global fitting (LIF and microwave). Hi-resolution LIF spectra of all other isotopomers.