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Phys Chem Chem Phys. 2014 Aug 14;16(30):15739-15751. doi: 10.1039/c3cp55352c.

Chirped-Pulse millimeter-Wave spectroscopy for dynamics and kinetics studies of pyrolysis reactions.

Author information

1
Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139, USA. prozument@mit.edu rwfield@mit.edu and Department of Chemistry, Wayne State University, 5101 Cass Ave, Detroit, MI 48202, USA.
2
Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139, USA. prozument@mit.edu rwfield@mit.edu.
3
Department of Chemistry and Biochemistry, Middlebury College, 276 Bicentennial Way, Middlebury, VT 05753, USA.
4
Department of Chemistry, Wayne State University, 5101 Cass Ave, Detroit, MI 48202, USA.
5
Department of Chemistry and Biochemistry, University of Colorado at Boulder, Cristol Chemistry 58, Boulder, CO 80309, USA.
6
Department of Chemistry, University of Rochester, 120 Trustee Road, Rochester, NY 14627, USA.
7
Department of Chemistry, The University of Texas at Austin, 1 University Station A5300, Austin, TX 78712-0165, USA.

Abstract

A Chirped-Pulse millimeter-Wave (CPmmW) spectrometer is applied to the study of chemical reaction products that result from pyrolysis in a Chen nozzle heated to 1000-1800 K. Millimeter-wave rotational spectroscopy unambiguously determines, for each polar reaction product, the species, the conformers, relative concentrations, conversion percentage from precursor to each product, and, in some cases, vibrational state population distributions. A chirped-pulse spectrometer can, within the frequency range of a single chirp, sample spectral regions of up to ∼10 GHz and simultaneously detect many reaction products. Here we introduce a modification to the CPmmW technique in which multiple chirps of different spectral content are applied to a molecular beam pulse that contains the pyrolysis reaction products. This technique allows for controlled allocation of its sensitivity to specific molecular transitions and effectively doubles the bandwidth of the spectrometer. As an example, the pyrolysis reaction of ethyl nitrite, CH3CH2ONO, is studied, and CH3CHO, H2CO, and HNO products are simultaneously observed and quantified, exploiting the multi-chirp CPmmW technique. Rotational and vibrational temperatures of some product molecules are determined. Subsequent to supersonic expansion from the heated nozzle, acetaldehyde molecules display a rotational temperature of 4 ± 1 K. Vibrational temperatures are found to be controlled by the collisional cooling in the expansion, and to be both species- and vibrational mode-dependent. Rotational transitions of vibrationally excited formaldehyde in levels ν4, 2ν4, 3ν4, ν2, ν3, and ν6 are observed and effective vibrational temperatures for modes 2, 3, 4, and 6 are determined and discussed.

PMID:
24756159
DOI:
10.1039/c3cp55352c
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