Reactions of the CN Radical with Benzene and Toluene: Product Detection and Low-Temperature Kinetics

Journal Article · Wed Dec 23 04:00:00 EST 2009 · Journal of Physical Chemistry A

OSTI ID:983203

Trevitt, Adam J; Goulay, Fabien; Taatjes, Craig A; Osborn, David L; Leone, Stephen R

Low temperature rate coefficients are measured for the CN + benzene and CN + toluene reactions using the pulsed Laval nozzle expansion technique coupled with laser-induced fluorescence detection. The CN + benzene reaction rate coefficient at 105, 165 and 295 K is found to be relatively constant over this temperature range, 3.9 - 4.9 x 10-10 cm3 molecule-1 s-1. These rapid kinetics, along with the observed negligible temperature dependence, are consistent with a barrierless reaction entrance channel and reaction efficiencies approaching unity. The CN + toluene reaction is measured to have a slower rate coefficient of 1.3 x 10-10 cm3 molecule-1 s-1 at 105 K. At room temperature, non-exponential decay profiles are observed for this reaction that may suggest significant back-dissociation of intermediate complexes. In separate experiments, the products of these reactions are probed at room temperature using synchrotron VUV photoionization mass spectrometry. For CN + benzene, cyanobenzene (C6H5CN) is the only product recorded with no detectable evidence for a C6H5 + HCN product channel. In the case of CN + toluene, cyanotoluene (NCC6H4CH3) constitutes the only detected product. It is not possible to differentiate among the ortho, meta and para isomers of cyanotoluene because of their similar ionization energies and the ~;; 40 meV photon energy resolution of the experiment. There is no significant detection of benzyl radicals (C6H5CH2) that would suggest a H-abstraction or a HCN elimination channel is prominent at these conditions. As both reactions are measured to be rapid at 105 K, appearing to have barrierless entrance channels, it follows that they will proceed efficiently at the temperatures of Saturn?s moon Titan (~;;100 K) and are also likely to proceed at the temperature of interstellar clouds (10-20 K).

• Research Organization: Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA (US)
• Sponsoring Organization: Chemical Sciences Division
• DOE Contract Number: AC02-05CH11231
• OSTI ID: 983203
• Report Number(s): LBNL-3333E
• Journal Information: Journal of Physical Chemistry A, Journal Name: Journal of Physical Chemistry A
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
99 GENERAL AND MISCELLANEOUS
BENZENE
BENZYL RADICALS
CLOUDS
DECAY
DETECTION
ENERGY RESOLUTION
FLUORESCENCE
IONIZATION
ISOMERS
KINETICS
MASS SPECTROSCOPY
NOZZLES
PHOTOIONIZATION
PHOTONS
RADICALS
REACTION KINETICS
Reactions
Radical
Benzene
Toluene
Low Temperature Kinetics
SYNCHROTRONS
TEMPERATURE DEPENDENCE
TOLUENE