Vibrational relaxation, dissociation, and dissociation incubation times in norbornene

Abstract

Shock waves in norbornene(bicyclo [2,2,1] hept-2-ene, C7HlO)-krypton mixtures have been examined with the laser-schlieren technique over the very wide range of conditions, 542-1480 K, and 34-416 Torr in 0.5%, 2%, and 4% C 7 H lO . The experiments exhibit both vibrational relaxation (542-1480 K) and the retro-Diels-Alder dissociation, norbornene---1,3-cyclopentadiene+ethylene (869-1480 K). Over 869-1304 K, and for pressures below 140 Torr, both relaxation and dissociation are resolved. These experiments provide the first measurements of unimolecular incubation (induction) times for the dissociation of a large polyatomic molecule. The ratio t/7 decreases from ~ 5 to 2 in 900-1300 K. Vibrational relaxation is rapid, 10glO P7 (flS atm) =0.066-6.70/T II3 , with a weak inverse temperature dependence, but is completely consistent with series excitation through the lowest-frequency mode. Dissociation shows very strong unimolecular falloff. A Rice-Ramsperger-Kassel-Marcus (RRKM) model, parametrized to fit the observations (E o =44.2 kcal/mol, (AE)down=280 cm-I ), finds the reaction closer to the low pressure limit ko than to koo for 1400 K and 100 Torr. Earlier work at low temperatures « 750 K) has Ea too low to extrapolate to the present results. Thus a significant increase in E: is indicated over 700-1000 K, suggesting a change in mechanism.

Collisional energy transfer in polyatomic molecules at high temperatures: Master equation analysis of vibrational relaxation of shock-heated alkanes

“…Kiefer and co-workers [13,14,[26][27][28] reported a series of vibrational relaxation studies of shock-heated hydrocarbons in krypton baths using LS densitometry. They observed fast vibrational relaxation times of a few tens to hundreds of ns atm [13,14,26], which displayed 'inverted' temperature dependences as a consequence of the large amounts of energy that must be transferred to reach vibrational equilibrium at high temperatures. These relaxation data enable investigation of the collisional energy transfer process at high temperatures that are relevant to combustion modeling.…”

“…A variety of spectroscopic methods, such as infrared fluorescence [6][7][8], ultraviolet absorption [9,10], kinetically controlled selective ionization [11,12], and laser schlieren (LS) densitometry [13,14], have been E-mail address: a.matsugi@aist.go.jp used to directly or indirectly measure the energy transfer rates of polyatomic molecules in collision with bath gases. These studies revealed that the energy transfer rate depends on the initial energy, bath temperature, and type of third-body collider.…”

Shock-tube study of relaxation in HCN

“…The analysis used herein is quite routine having now been used in several previous relaxation studies from this laboratory. [21][22][23][24][25] One interesting feature seen in these low-pressure experiments was the consistent appearance of a slower late gradient, as is most evident in the semilog plot of the 790 K, 22 Torr experiment in Fig. 1.…”

Energy transfer in master equation simulations: A new approach

“…To extract quantitative Figure 6 Simulation of norbornene decomposition in shock waves. The conditions correspond to Shock #76 reported by Kiefer et al [44] and modeled previously by Barker and King [36]. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.…”

“…Tests were carried out by using two constant values of the energy transfer parameter α(y) for ClOOCl (small molecule, colliding with N 2 ) and for 1,1,1-trifluoroethane (intermediate size, colliding with Kr). Tests carried out for norbornene (large molecule, colliding with Kr) employed an energy-dependent parameter α(y) found from an analysis [36] of shock tube experimental data [44].…”