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Part 1 The Cavity FTMW Spectrometer with Double Resonance Application of Double Resonance Part2 Formic and Propiolic Acid Dimer Part 3 Trans Methyl Formate The FTMW Spectrometer is powerful tool used in rotational spectroscopy, it is used to determine molecular structure by observing the rotational transitions in the microwave spectrum. Balle, T.J.; Flygare, W.H. Fabry–Perot cavity pulsed Fourier transform microwave spectrometer with a pulsed nozzle particle source. Rev. Sci.Instrum. 1981, 52 (1), 33–45. Narrow Band (Cavity) Chirped Broadband Spectrometer Advantage Advantage Disadvantage Enhanced Signal Slow for large bandwidth Large Frequency Range More power Polarizing Pulse, more power Multiple gas nozzle Loss of signal Disadvantage Narrow Bandwidth Amplification of Emission Expensive electronics In expensive Highly reliant on Phase stability Fast for monitoring one line Wolfgang Jaeger, University of Alberta 1. Pulse molecular beamAdiobatic expansion occurs which cools the molecules 2. MW pulse - Polarizes the molecules at Resonant Transition 3. Polarized gas coherently emits at resonant frequencies 4. Signals detected in superheterodyne detector and a Fourier Transform is done to give Spectrum http://www.chem.ualberta.ca/~jaeger/research/ftmw/ftmw.htm A Rotational Transition is monitored. 2. Cavity is scanned with a second frequency that is resonant with monitored state. Coherence is destroyed if the second frequency shares a similar quantum state with the monitored frequency. 3. This coherence disruption is shown by a depletion in intensity. 1. 505 Linked Map of Quantum States 404 303 202 515 414 313 212 413 Frequency Range Extension Checking assignment of rotational spectra of molecules which helps to identify molecules. Double Resonance Monitor- A-Type 16430 MHz Scan- B-type 15498.34MHz and the quantum mechanics behind tunneling Carboxylic Acid Dimer Formation •Investigation of the acid dimer formation by understanding the tunneling motion of the hydrogen bonds. •The use of the cavity and double resonance will help identify the weaker Btype transitions on an already weak dipole since it has a weak dipole of .08 D. •The B-type transitions are important to monitor, because they allow the tunneling rate to be calculated. •By understanding the rate of proton tunneling, hydrogen bonds in biological systems can be better understood. Applications •Understand the rate of tunneling in the hydrogen bond. •Signaling mechanisms in bio-systems; proteins and enzymes. • The hydrogen bonds that make up DNA. Acid Dimer Formation X Y Formic Acid The rate at which the two protons tunnel across creates the hydrogen bond and the dimer formation. X Y Propiolic Acid Tunneling Motion: Classics vs. Quantum Classically the motion of a particle through a barrier suggests that given a certain energy it would not be able to pass though it. According to quantum mechanics the wave like nature of particles allows them to pass through barriers. The lower the barrier the less the particles have to go through and the greater chance of passing though. This is called tunneling. H H EHydrogen < EBarrier Only part of the wave makes it though. Left Potential Well X Y E Right Potential Well X Y E Tunneling E E Symmetric Double Well Tunneling E E O- Asymmetric O+ Symmetric The wave functions of the two different forms interact to give the splitting according to quantum mechanics. Vibrational Transitions from the Tail EE •Even though there is splitting, the transitions between the splitting can not always be observed. •The dimer has a long chain on the propiolic acid which allows it to have a change in dipole as the tunneling process takes place. •The change in dipole allows there to be some vibrational transitions going from the O+ to the Ostates. •The end result: splitting occurs from the predicted frequency on the spectrometer. •The rate of tunneling can be calculated by the amount of splitting. A A O- Asymmetric O+ Symmetric Addition of Deuterated Form •The use of the deuterated form of the dimer causes the mass that undergoes tunneling to change from 2 amu to 4 amu and lowers the rate of tunneling. EE •The zero point energy of the dimer lowers and also causes the tunneling rate to slow. •The addition of the deuterium lowers the rate by about 67 times. Normal Acid Dimer Deuterated Acid Dimer Hydrogens Normal Form Deuteriums Deuterated Form Procedure: Set up •Cavity was equipped with a reservoir to hold the acids instead of being inside of a gas tank. •Neon gas was passed over the sample to deliver the molecules into the chamber. •A 1:2 ratio of formic to propiolic acid was used. Procedure: Frequencies Deuteriums Calculated Frequencies Formic (OD)-Propiolic (OH) 505-404 8585.926 MHz 606-505 10278.184 MHz Formic (OH)-Propiolic (OD) 505-404 8567.293 MHz 606-505 10256.123 MHz Formic (OD)-Propiolic (OD) 505-404 8540.464 MHz 606-505 10222.995 MHz Double Resonance 515-404 12613.528 MHz 615-505 14001.597 MHz While monitoring the double deuterated 606 to 505 transition at 10222.99 MHz, double resonance was used to investigate a few MHz away from the predicted center. Results Calculated Frequencies Formic (OD)-Propiolic (OH) 505-404 8585.926 MHz 606-505 10278.184 MHz Formic (OH)-Propiolic (OD) 505-404 8567.293 MHz 606-505 10256.123 MHz Formic (OD)-Propiolic (OD) 505-404 8540.464 MHz 606-505 10222.995 MHz Double Resonance 515-404 12613.528 MHz 615-505 14001.597 MHz Predicted: 14001.597 MHz The splitting occurred 14005.0 MHz and 13998.2 MHz While monitoring the 606 to 505 transition at 10222.99 MHz, double resonance was used to investigate a few MHz away from the predicted center. •The predicted splitting about 3.4 MHz away for the double deuterated form. •From prior experiments the pure hydrogen form, the splitting occurred 291 MHz away. •To confirm this hypothesis the 717 to 606 transition was investigated. Conclusion •The slitting occurs about 3.4 MHz from the predicted frequency for the double deuterated form. •The higher the activation barrier the more difficult for the dimer to tunnel. •A change in mass that undergoes tunneling will effect the tunneling motion. •The H-C ≡C- allows there to be transitions between the vibrational states of the splitting. 3.4 MHz Predicted Quantum Splitting E E Deuteriums Normal Acid Dimer Deuterated Acid Dimer Overall Goal of CCU & Summer Research High Abundance of MF in space. Spatial Map of Orion Nebula* Horn et al. (2004)** propose following reaction pathways [CH3OH2]+ + H2CO [HC(OH)OCH3]+ + H2 H2C=O + [H2C=O-H]+ [HC(OH)OCH3]+ + hv [CH3OH2]+ + CO [HC(OH)OCH3]+ + hv CH3+ + HCOOH [HC(OH)OCH3]+ + hv Probable Reaction: [CH3OH2]+ + HCOOH HC(OH+)OCH3 *S.-Y. Liu, J.M. Girart, A. Remijan, and L.E. Snyder, Ap.J., 576 (2002) 255-263. **A. Horn et al., Ap.J., 611 (2004) 605-614 + H2O trans µa = 4.1 D (ab initio) µb = 2.8 D (ab initio) A = 47354.28 MHz B = 4704.440 MHz C = 4398.435 MHz V3 = 14.9 cm-1 cis µa = 1.63 D (Bauder 1979) µb = 0.68 D (Bauder 1979) A = 19985.71 MHz (Curl 1959) B = 6914.63 MHz (Curl 1959) C = 5304.47 MHz (Curl 1959) V3 = 398.76 cm-1 (Oesterling et al 1998) Green: Monitored Frequencies Yellow: Second Scanning Frequencies Four methods of identifying trans lines in the lab & in space: 1. Do the lines belong to the same species? 2. Do the lines appear in the Broadband spectrum? 3. Are the experimental data & ab initio a good fit? 4. Do the lines appear in space? DR Monitored Monitored DR Parameter Experimental Ab Initio A (MHz) 47357(320) 46543.42 B (MHz) 4704.44(6) 4732.99 C (MHz) 4398.434(1) 4417.46 ΔJ(kHz) 1.1(1) ΔJK (kHz) -124(9) δJ (kHz) 0.108(5) ΔKm (MHz) -163(61) ΔJm (MHz) 0.92(8) δm (MHz) -1.6(6) V3 (cm-1) 14.9(6) 22.6 θtop (deg)a 23.49(16) 26.0 Iα (amu Å2) 3.18(6) 3.149 Nlines 28 rms error (kHz) 35 Fit with XIAM H. Hartwig and H. Dreizler, Z. Naturforsch 51a (1996) 923-932. Temperature (K) Detection of trans-Methyl Formate in Sagitarius-B2(N) Green Bank Telescope PRIMOS Project, available on the Internet at http://www.cv.nrao.edu/~aremijan/PRIMOS. Double Resonance is an effective technique in identifying weak transitions. Double Resonance can be used in understanding tunneling in Carboxlyic Acid Dimers. Trans-Methyl Formate is found in Space! 1. 2. 3. 4. 5. D.A. Andrews, J.G. Baker, B.G. Blundell and G.C. Petty, 3. Mol. Stmcr., 97, 1983, 271-83. T.J. Balle, W.H. Flygare, Rev. Sci. Instrum. 1981, 52 (1), 33–45. A. Bauder, M. et al., Chemical Physics Letters, 144, 1988, 2. J. Ekkers and W.H. Flygare, Rev. Sci. Instr. 47, 1976, 448. K.O. Douglass, New FTMW Techniques for DRS. Thesis. University of Virginia, 2007. Personal Thanks to: Brooks Pate Matt Muckle Justin Neill Amanda Steber NSF Division of Human Resource Development Louis Stokes Alliance for Minority Participation program (HRD-0703554) NSF Division of Chemistry Centers for Chemical Innovation program (CHE-0847919) Brooks Pate Matt Muckle Sara Fitzgerald Justin Neill Amanda Steber Danny Zaleski Marcus Martin Kristin Morgan Shirley Cauley Anthony Remijan Robin Pulliam