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ROTATIONALLY RESOLVED ELECTRONIC SPECTRA OF SECONDARY ALKOXY RADICALS 06/22/10 JINJUN LIU AND TERRY A. MILLER Laser Spectroscopy Facility Department of.

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Presentation on theme: "ROTATIONALLY RESOLVED ELECTRONIC SPECTRA OF SECONDARY ALKOXY RADICALS 06/22/10 JINJUN LIU AND TERRY A. MILLER Laser Spectroscopy Facility Department of."— Presentation transcript:

1 ROTATIONALLY RESOLVED ELECTRONIC SPECTRA OF SECONDARY ALKOXY RADICALS 06/22/10 JINJUN LIU AND TERRY A. MILLER Laser Spectroscopy Facility Department of Chemistry The Ohio State University PREDICTION AND DETERMINATION OF SPIN-ROTATION CONSTANTS OF NEARLY DEGENERATE ELECTRONIC STATES

2 ethoxy …… methoxy CH 3 O CD 3 O CH 2 DO CHD 2 O ethoxy iso-propoxy 1-propoxy 2-butoxy cyclohexoxy …… Alkoxy radicals (RO·)

3 PES Normal JT (linear only) JT w/ SO (CH 3 O, CD 3 O) JT w/ SO & asym. deuteration (CH 2 DO, CHD 2 O)

4 Lifting of Vibronic Degeneracy: a qualitative view C O H CsCs  A’ D D C O H CsCs  A” H H C 3v E D D

5 Excimer Laser (XeCl) Pulse Dye Amplifier Ar + Laser CW Ring Dye Laser Computer XeF Photolysis Laser PMT Doubling Crystal Hi-resolution LIF apparatus Box- Car Etalon PD I2I2 Lock- in RONO+He LIF = laser-induced fluorescence T~1K spectral linewidth ~ 200 MHz frequency accuracy ~ 50 MHz

6 ground stateexcited state Hamiltonian H = H Rot + H SR H = H Rot H Rot = AN a 2 + BN b 2 + CN c 2 H SR = ½  ab (N a S b + S b N a ) molecular constants rotational constants A", B", C" A', B', C' spin-rotation constants  aa ",  bb ",  cc " ½(  ab " +  ba " ) transition types ½(  ac " +  ca " ) a:b:c ½(  bc " +  cb " )      ethoxy Spectroscopic model “Rotationally Resolved Electronic Excitation Spectra of the Ethoxy B  X Transition”, X. Q. Tan, J. M. Williamson, S. C. Foster, and T. A. Miller, J. Phys. Chem. 97, 9311 (1993). c b a transition types a:b:c=0:0:1

7 y z x y z x b a c b a c URUR USUS Hamiltonian and prediction of spin-rotation tensor ethoxy (R) T 1-propoxy (S) “The isotopic dependence of the spin-rotation interaction for an asymmetric top molecule”, J. M. Brown, T. J. Sears and J. K. G. Watson, Mol. Phys. 41, 173 (1980) "Theoretical Prediction of Spectroscopic Constants of 1-alkoxy Radicals." G. Tarczay, S. Gopalakrishnan, and T. A. Miller, J. Mol. Spectros., 220, 276, (2003). ``Rotationally Resolved - Electronic Spectra of Both Conformers of the 1- Propoxy Radical,'', S. Gopalakrishnan, C. C. Carter, L. Zu, V. Stakhursky, G. Tarczay and T. A. Miller, J. Chem. Phys., 118, 4954 (2003). Spin-rotation constants of 1-propoxy in GHz Rot: rotational SR: spin-rotation T: trans- G: gauche- “geometry-fixed coordinate system”principal axis system ground (X) stateexcited (B) state H = H Rot + H SR H = H Rot H Rot = AN a 2 + BN b 2 + CN c 2 H SR = ½  αβ (N α S β + S β N α ) R: reference; S: substituted  

8 in cm -1 ethoxyiso-propoxy Calc. w/o ZPE w/o ΔE PJT (C s -C s )+335-122 w ΔE PJT (C 1 -C s )+340-24 w/ ZPE+508-46 Expt. † +355(10)-68(10) Ethoxy v.s. iso-propoxy tilt angle of O from C s plane (degree) PJT: pseudo-Jahn-Teller tilt angle of O from C s plane (degree) ΔE PJT =98 cm -1 † " Dispersed Fluorescence Spectroscopy of Primary and Secondary Alkoxy Radicals," J. Jin, I. Sioutis, G. Tarczay, S. Gopalakrishnan, A. Bezant, T. A. Miller, J. Chem. Phys. 121, 11780 (2004).

9 in cm -1 ethoxyiso-propoxy Calc. w/o ZPE w/o ΔE PJT (C s -C s )+335-122 w ΔE PJT (C 1 -C s )+340-24 w/ ZPE+508-46 Expt. † +355(10)-68(10) Iso-propoxy v.s. ethoxy PJT: pseudo-Jahn-Teller ΔE PJT =98 cm -1 † " Dispersed Fluorescence Spectroscopy of Primary and Secondary Alkoxy Radicals," J. Jin, I. Sioutis, G. Tarczay, S. Gopalakrishnan, A. Bezant, T. A. Miller, J. Chem. Phys. 121, 11780 (2004). iso-propoxy ethoxy

10 “geometry-fixed coordinate system”“orbital-fixed coordinate system” Common coordinates for prediction of SR tensor

11 a.Geometry optimized at the B3LYP/6-31G* level of theory and used to calculate U s. b.At the CIS/6-31G* level of theory. c.In the “geometry-fixed coordinate system”. Scaled by A-X separation. d.In the “orbital-fixed coordinate system”. Scaled by A-X separation. Molecular constants of iso-propoxy in cm -1. Iso-propoxy y(a)y(a) z x b c transition types a:b:c=0:0:1

12 G+ 2-butoxy G- 2-butoxy 2-butoxy "High Resolution Spectra and Conformational Analysis of 2-Butoxy Radical," V. Stakhursky, L. Zu, J. Liu and T. A. Miller, J. Chem. Phys, 125, 094316 (2006) G+TG- expt.125(10)55(10)

13 a.Geometry optimized at the UHF/6-31+G* level of theory. b.At the CIS/6-31+G* level of theory. Molecular constants of T 2-butoxy in GHz. T conformer of 2-butoxy transition types a:b:c=2:0:3 =68(10) cm -1 55(10) cm -1

14 Cyclohexoxy A’ F’ C’ E’ G’ J’ Bands labeled in circles: Type II A F C E G B DH J K I Bands labeled in squares: Type I64.4(4) cm -1 cyclohexoxy

15 Cyclohexoxy Transition Type I Transition Type II Primed Bands AFAF BF’

16 Cyclohexoxy a.At the B3LYP/6-13+G* level of theory. b.At the CIS/6-31+G* level of theory. Molecular constants of cyclohexoxy in GHz. a:b:c=1:0:0 a:b:c=0:1:0

17 Cyclohexoxy a.Geometry optimized at the B3LYP/6-31+G* level of theory. b.At the CIS/6-31+G* level of theory. Molecular constants of cyclohexoxy in GHz. a:b:c=1:0:0a:b:c=0:1:0 B  X transition to a’ vibronic level (origin band) B  X transition to a” vibronic levelB  A transition to a’ vibronic level

18 SR of secondary alkoxies isopropoxyT-2-butoxycyclohexoxy ε xx 233167 ε yy 23699 ε zz -342-218 |ε xz +ε zx |/22 iso-propoxyT 2-butoxycyclohexoxy

19 Summary and Future work  Explanation to perturbed transitions and anomalous line intensities in the spectra of cyclohexoxy and T 2-butoxy.  Physical mechanism of spin-rotation constants for nearly degenerate electronic states.  Explanation to perturbed transitions and anomalous line intensities in the spectra of cyclohexoxy and T 2-butoxy.  Physical mechanism of spin-rotation constants for nearly degenerate electronic states.  Spin-rotation tensor of iso-propoxy predicted in an “orbital- fixed coordinate system” using ethoxy as a reference molecule;  Spin-rotation tensors of T 2-butoxy and cyclohexoxy predicted based on the experimental result of 2-propoxy;  Hi-resolution LIF spectra of iso-propoxy, T 2-butoxy and cyclohexoxy simulated using the ab initio calculated rotational constants and predicted spin-rotation constants;  Transition types determined experimentally confirms the symmetry of electronic states predicted by ab initio calculations.  Spin-rotation tensor of iso-propoxy predicted in an “orbital- fixed coordinate system” using ethoxy as a reference molecule;  Spin-rotation tensors of T 2-butoxy and cyclohexoxy predicted based on the experimental result of 2-propoxy;  Hi-resolution LIF spectra of iso-propoxy, T 2-butoxy and cyclohexoxy simulated using the ab initio calculated rotational constants and predicted spin-rotation constants;  Transition types determined experimentally confirms the symmetry of electronic states predicted by ab initio calculations.

20 Dr. Phillip S. Thomas NSF $$$ NSF $$$ Thank you all! Thank you all! Miller Group Acknowledgements

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