YUAN-PERN LEE LABORATORY

Welcome to the YPlaboratory

Shock Tube Technique

Introduction

     The shock tube is the best tool for kinetic experiments in the gaseous phase at high temperatures because it can generate a uniform high-temperature environment. Its operation utilizes a pressure difference to produce the shock wave; then the shock wave compresses the gas in the reactor. We utilize this technique to study the kinetics of reactions; current projects involve reactions of oxygen atoms with other molecules. Oxygen atoms are generated by pyrolysis of N2O or photolysis of SO2; their concentration is detected by vacuum-ultraviolet(VUV) atomic-resonance absorption spectroscopy (ARAS) conventional system produces a shock wave an puncturing of a diaphragm that separates the regions of large and small pressures . Because our experimental system utilizes a diaphragmless piston driver, it is unnecessary to open the reactor so that it becomes contaminated an exposure to ambient air; it can produce a temperature about 2000 K; this characteristic is important in high-temperature research. The shock wave is almost the only choice for research.

Recent Projects

     Methanol (CH3OH) is considered an important alternative fuel; it can be used directly in an internal-combustion engine or in a fuel cell via catalytic electrolytic reactions. The reaction
     O(3P) + CH3OH    –> OH + CH2OH            (1a)
                                   –> OH + CH3O              (1b)
                                   –> HO2 + CH3               (1c)
with these energetically accessible channels is an important process in combustion of CH3OH. The branching between these channels plays an important role in the formation of the end products.

Experiment

     Rate coefficients of the reaction O(3P) + CH3OH in the temperature range 835-1777 K were determined. O atoms were generated by photolysis of SO2 with a KrF excimer laser at 248 nm or an ArF excimer laser at 193 nm; temporal profiles of their concentration were monitored via atomic resonance absorption spectroscopy using a microwave-discharged oxygen lamp.

  1. Shock tube
    1. Low-pressure reactor section：electroplated stainless steel tube (i. d. 7.6 cm，length 5.9 m)
    2. High-pressure driver section：main piston, sub-piston
    3. Vacuum pumps：turbo molecular pump (Varian，Turbo-V 700HT) and dry-scroll vacuum pump (Varian，Triscroll 300) to reach an ultimate pressure 10-7 torr.
  2. Detection system
    1. pressure sensors and time-frequency counters：to determine the velocity of the shock wave
    2. microwave-discharged lamp: as a  VUV light source
    3. vacuum UV monochromator and solar-blind photomultiplier tube: to detect light at a specific wavelength
    4. signal amplifier and oscilloscope: to record temporal profile of the signal
OMPUTATIONAL METHODS ( in collaboration with Prof. M. C. Lin at Emory Univ. , USA)

     Rate coefficients were calculated with conventional transition state theory (TST), canonical variational transition-state theory (CVT) with zero-curvature-tunneling corrections (ZCT) and small-curvature-tunneling corrections (SCT) using the POLYRATE program of Truhlar et al.RESULTS AND DISCUSSION
A typical temporal profile observed after irradiation of a sample containing SO2 (300 ppm) and CH3OH (200 ppm) in Ar is shown below (T = 1372 K and total density = 8.791018 molecule cm-3). The thick solid line represents fitted results.

Publications

  1. Experimental and theoretical studies of rate coefficients of the reaction O(3P) + HCl at high temperatures, C.-C. Hsiao, Y.-P. Lee, N. S. Wang, J. H. Wang, and M. C. Lin, J. Phys. Chem. A. 106, 10231 (2002).
  2. Experiments and Calculations on Rate Coefficients for Pyrolysis of SO2 and the Reaction O + SO at High Temperatures, C.-W. Lu, Y.-J. Wu, Y.-P. Lee, R. S. Zhu, and M. C. Lin, J. Phys. Chem. A 107, 11020 (2003).
  3. Experimental and theoretical studies of rate coefficients for the reaction O(3P) + CH3OH at high temperatures, C.-W. Lu, S.-L. Chou, Y.-P. Lee, S. Xu, Z. F. Xu, and M. C. Lin, J. Chem. Phys. 122, 244314 (2005).
  4. Kinetics of the reactions of CS2OH with O2, NO, and NO2, E. W.-G. Diau and Y.-P. Lee, J. Phys. Chem. 95, 7726 (1991).
  5. Detailed rate coefficients and the enthalpy change of the equilibrium reaction OH+C2H4–>HOC2H4 over the temperature range 544673 K, E. W.-G. Diau and Y.-P. Lee, J. Chem. Phys. 96, 377 (1992).
  6. Experimental and theoretical investigations of rate coefficients of the reaction S(3P) + O2 in the temperature range 298-878 K, C.-W. Lu, Y.-J. Wu, Y.-P. Lee, R. S. Zhu, and M. C. Lin, J. Chem. Phys. 121, 8271 (2004).