Chirped Pulse Microwave Spectroscopy on Methyl Butanoate Alicia
Chirped Pulse Microwave Spectroscopy on Methyl Butanoate Alicia Hernandez-Castillo, Brian Hays, Chamara Abeysekara, and Timothy Zwier
Motivation • Methyl Butanoate has the major groups to compare to biofuels • The decomposition products can proceed through several channels • The oxidative chemistry has been modelled before
Theory • Conformational search performed with the MM 2* force field using Macro. Model • Optimized structures at the MP 2/aug-cc-p. VTZ level of theory using Guassian 09 with ZPVE pt gg tt tg
Experimental Guzik 40 GS/s digitizer 13 GHz bandwidth
Experimental
Spectrum 1. 5 million averages 25 averages/gas pulse 10% TWTA Gain 15 PSI He
Conformation-Specific Spectroscopy • The initial analysis was done using Strong Field Coherence Breaking technique to find which transitions belonged to which conformer • Will be discussed in full detail in tomorrow’s talks
Conformation-Specific Spectroscopy • The initial analysis was done using Strong Field Coherence Breaking TG 03 and TG 04 in the technique to find which transitions Spectroscopy in Atmospheric belonged to which Chemistry Mini-Symposium conformer Tuesday afternoon • Will be discussed in full detail in tomorrow’s talks
Spectrum
Tunneling Splitting Fit using the XIAM program C. C. Lin and J. D. Swalen, Rev. Mod. Phys. 31, 841 -892 (1959) H. Hartwig and H. Dreizler, Z. Naturforsch 51 a, 923 -932 (1996)
Methyl rotor Tunneling Splitting E A E Conformer tt E A Conformer tg A * A
Methyl rotor Tunneling Splitting E A E Conformer tt E A Conformer tg A * A
Methyl rotor Tunneling Splitting E A E E&A Conformer tt E A E A E Conformer 2 A * A
Internal Rotor Fit Experimental Theoretical A (MHz) 8349. 7639(25) 8377. 873 B (MHz) 1197. 763(13) 1206. 8277 C (MHz) 1076. 547(91) 1082. 9548 DJ (k. Hz) 0. 052(20) DJK (k. Hz) 0. 039784 d. J (k. Hz) 0. 0117(24) V 3 (cm-1) 395(24) F 0 (GHz) 150. 3(8. 0) epsilon (rad) -2. 67 (20) delta (rad) 0. 468(85) N 32 rms (MHz) 0. 040843 Jmax 12 tt conformer
Internal Rotor Fit A (MHz) B (MHz) C (MHz) DJ (k. Hz) DJK (k. Hz) DK (k. Hz) d. J (k. Hz) V 3 (cm-1) F 0 (GHz) epsilon (rad) delta (rad) N rms (MHz) Jmax Experimental 6059. 353(17) 1421. 3492(24) 1333. 3682(28) 0. 477(38) -6. 03(26) 51. 5(2. 3) -0. 083(29) 426(16) 160. 8(5. 3) -6. 02(32) 0. 5404(49) 47 0. 029952 7 Theoretical 5828. 7687 1450. 984 1379. 7689 tg conformer
Conformers Found • No Conformer gg or pt found • No evidence for more conformers pt gg tt tg
Conformers Found • No Conformer gg or pt found • No evidence for more conformers Conformational Cooling pt gg tt tg
Relative Populations • Using rotation diagram method with the form: J. M. Oldham, C. Abeysekara, et al. J. Chem. Phys. 141, 154202 (2014)
Relative Populations tt 40% tg 60%
Future Work • Are more conformers available in the jet cooled spectrum • Look for more conformers and excited vibrational states in room temperature cell • Pyrolysis on methyl butanoate to look for radicals such as:
Acknowledgements The Zwier Group #55152 -ND 6
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