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OBSERVATION OF VIBRATIONALLY HOT CH 2 CHO IN THE 351 NM PHOTODISSOCIATION OF XCH 2 CH 2 ONO (X=F,Cl,Br,OH) Rabi Chhantyal-Pun, Ming-Wei Chen, Dianping.

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Presentation on theme: "OBSERVATION OF VIBRATIONALLY HOT CH 2 CHO IN THE 351 NM PHOTODISSOCIATION OF XCH 2 CH 2 ONO (X=F,Cl,Br,OH) Rabi Chhantyal-Pun, Ming-Wei Chen, Dianping."— Presentation transcript:

1 OBSERVATION OF VIBRATIONALLY HOT CH 2 CHO IN THE 351 NM PHOTODISSOCIATION OF XCH 2 CH 2 ONO (X=F,Cl,Br,OH) Rabi Chhantyal-Pun, Ming-Wei Chen, Dianping Sun, Terry A. Miller

2 Motivation XRONO are chemical precursors for XRO (alkoxy) radicals OH substituted alkoxy radicals are important intermediate in atmospheric oxidation of alkenes like ethene, butadiene and isoprene HOCH 2 CH 2 O radical is a prototypical hydroxyalkoxy radical Halogen substituted ethoxy can be a model for the study of HOCH 2 CH 2 O radical S. Sawada and T. Totsuka, Atmos. Environ. 20, 821 (1986)

3 Experimental technique ~~ Laser Induced Fluorescence (LIF) method has been used in the past to study the B-X transition of alkoxy radicals LIF coupled with supersonic free jet expansion produces rotationally cold spectrum; high resolution LIF spectrum can be used to obtain rotational constants and geometry of alkoxy radicals. Gopalakrishnan et. al. JCP 118 4954 1-Propoxy

4 XCH 2 CH 2 ONO / He General Valve ControllerDG535 Pulse Generator XeF Excimer Laser Nd:YAG Laser Sirah Dye Laser Nozzle T0T0 PMT Q-Switch Flash Lamp T 0 / GPIB T0T0 Lens Frequency Doubler Precursor preperation: XCH 2 CH 2 OH/H 2 SO 4 /NaNO 2 Experimental apparatus XCH 2 CH 2 O NO

5 ClCH 2 CH 2 ONO / FCH 2 CH 2 ONO 1 Gopalakrishnan et. al J. Chem. Phys. 118 (2003) 49–54 2 MSS 2011 FE09 HCHO AlkoxyExp. 1-Propoxy G 1 28634 1-Propoxt T 1 29219 FEO-G 2 29869 FEO-T 2 30519 ClEO-G28786 ClEO-T FCH 2 CH 2 O AlkoxyCO str. Ethoxy603 Prpoxy-G596 FEO-G604 546

6 A E C D B G F Unknown species identified L. R. Brock and E. A. Rohlfing JCP 106 10048 (1997) -ClCH 2 CH 2 ONO

7 HCHO from different XCH 2 CH 2 ONO SimulationExperiment

8 Cl Br F OH Vinoxy from XCH 2 CH 2 ONO Exp. Sim. -Larger power broadening in F and OH substituted nitrite due to higher laser power used (to overcome lower S/N)

9 Rotational temperature HCHO and CH 2 CHO fragments show similar rotational temperature pattern for different substituted nitrites. Rotational temperature (K) PrecursorHCHOCH 2 CHO HOCH 2 CH 2 ONO2.01 BrCH 2 CH 2 ONO2.6<2 ClCH 2 CH 2 ONO4.54 FCH 2 CH 2 ONO7.55

10 a g f e d c b i j h k * * F Cl Br OH Vibrational hot bands of Vinoxy from various XCH 2 CH 2 ONO * Bands not assgined to Vinoxy

11 Hot band assignments Exp. ModeDescriptionXBB-X 7C1H1H3 rock11431122-21 8C1C2 st957917-40 9C1C2O bend500449-51 12C1C2 torsion404274(x2=548)-130 L. R. Brock and E. A. Rohlfing JCP 106 10048 (1997)

12 Relative number density of HCHO/Vinoxy φ = Quantum yield for fluorescence = Probability of transition N = Number density S = Fluorescence signal F = Formadehyde V = Vinoxy R. G. Miller and E. K. C. Lee J. Chem. Phys. 68, 4448, (1978) (φ for HCHO) L. R. Brock and E. A. Rohlfing J. Chem. Phys. 106, 10048, (1997) (φ for Vinoxy, Lifetime for B state) D. T. Co et. al. J. Phys. Chem. A 109, 10675, (2005) (σ for HCHO) J. M. F. V. Dijk et. al. J. Chem. Phys. 69, 2453, (1978) ( value for HCHO) CASSCF/ 6-31G(d,P) ( value for Vinoxy) theo. exp. PrecursorS V /S F (LIF signal) N V /N F X10 3 (exp.) N V /N F X10 3 (theo.) HOCH 2 CH 2 ONO0.29±0.010.090.03 FCH 2 CH 2 ONO1.49±0.220.480.13 ClCH 2 CH 2 ONO4.55±0.451.460.40 BrCH 2 CH 2 ONO9.09±1.362.910.79

13 Photo-fragments formation mechanism Rx n 1 Rx n 2 Rx n 3

14 HCHO formation (Rx n 1) RadicalCalculated barrier 2 for Rx n I HOCH 2 CH 2 O9.2 FCH 2 CH 2 O15.1 ClCH 2 CH 2 O14.2 BrCH 2 CH 2 O15.9 - 1 J. Heicklen Advances in Photochemistry Volume 14 Pg. 177 - 2 CBS-QB3 method (most stable confomeric geometry used) RO-NO BDE: 40 kcal/mol 1 Maximum energy available after 351nm photo- dissociation: 41.5 kcal/mol Dissociation barrier for Rx n 1: ~15 kcal/mol HCHO should be formed primarily due to the secondary dissociation of XCH 2 CH 2 O radical

15 Vinoxy formation (Rx n 2 and Rx n 3) Calculation of barrier for HX elimination from XCH 2 CH 2 O (Rx n : 2) Preliminary result from collaboration with Laurie Butler group shows the internal energy left over in the radical would be less than the barrier calculated Non classical mechanisms like roaming could be in effect (Roaming have been observed in a similar radical HOCH 2 CH 2 dissociating to H 2 O and CH 2 CH) 2 Calculation of barrier for Rx n 3 (HX elimination from XCH 2 CH 2 ONO) is ongoing RadicalCalculated barrier 1 for Rx n 2 HOCH 2 CH 2 O36.13 FCH 2 CH 2 O39.74 ClCH 2 CH 2 O38.2 BrCH 2 CH 2 O34.62 1 B3LYP/6-311+g(d,p) method (most stable confomeric geometry used) 2 E. Kamarchik et. al. J. Phys. Chem. Lett. 1, 3058, (2010)

16 Conclusion CH 2 CHO and HCHO fragments are produced following 351nm photo-dissociation of XCH 2 CH 2 ONO (X= OH, F, Cl, Br); CH 2 CHO fragments produced are vibrationally hot HCHO is produced from the ground state dissociation of XCH 2 CH 2 O radical CH 2 CHO formation mechanism is still being studied

17 Acknowledgement Miller group members -Prof. Terry Miller -Dr. Dmitry Melnik -Dr. Dianping Sun -Dr. Mourad Roudjane -Dr. Takashige Fujiwara -Neal Kline -Terrance Codd -Meng Huang

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