Direct detection of pyridine formation by the reaction of CH (CD) with pyrrole: a ring expansion reaction
The reaction of the ground state methylidyne radical CH (X2Pi) with pyrrole (C4H5N) has been studied in a slow flow tube reactor using Multiplexed Photoionization Mass Spectrometry coupled to quasi-continuous tunable VUV synchrotron radiation at room temperature (295 K) and 90 oC (363 K), at 4 Torr (533 Pa). Laser photolysis of bromoform (CHBr3) at 248 nm (KrF excimer laser) is used to produce CH radicals that are free to react with pyrrole molecules in the gaseous mixture. A signal at m/z = 79 (C5H5N) is identified as the product of the reaction and resolved from 79Br atoms, and the result is consistent with CH addition to pyrrole followed by Helimination. The Photoionization Efficiency curve unambiguously identifies m/z = 79 as pyridine. With deuterated methylidyne radicals (CD), the product mass peak is shifted by +1 mass unit, consistent with the formation of C5H4DN and identified as deuterated pyridine (dpyridine). Within detection limits, there is no evidence that the addition intermediate complex undergoes hydrogen scrambling. The results are consistent with a reaction mechanism that proceeds via the direct CH (CD) cycloaddition or insertion into the five-member pyrrole ring, giving rise to ring expansion, followed by H atom elimination from the nitrogen atom in the intermediate to form the resonance stabilized pyridine (d-pyridine) molecule. Implications to interstellar chemistry and planetary atmospheres, in particular Titan, as well as in gas-phase combustion processes, are discussed.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- Chemical Sciences Division
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 983158
- Report Number(s):
- LBNL-3290E; ISSN 1463-9084; TRN: US1004565
- Journal Information:
- Physical Chemistry Chemical Physics, Journal Name: Physical Chemistry Chemical Physics; ISSN 1463-9076
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ATOMS
BROMOFORM
CHEMISTRY
COMBUSTION
DETECTION
EFFICIENCY
EXCIMER LASERS
GROUND STATES
HYDROGEN
LASERS
MASS SPECTROSCOPY
NITROGEN
PHOTOIONIZATION
PHOTOLYSIS
PLANETARY ATMOSPHERES
PYRIDINE
PYRROLES
RADICALS
REACTION KINETICS
RESONANCE
SYNCHROTRON RADIATION
Direct detection
pyridine formation
pyrrole
ring expansion