Large cross section for super energy transfer from hyperthermal atoms to ambient molecules

Abstract

The first experimentally measured cross-section for super energy transfer collisions between a hyperthermal H atom and an ambient molecule is presented here. This measurement substantiates an emerging energy transfer mechanism with significant cross-section, whereby a major fraction of atomic translational energy is converted into molecular vibrational energy through a transient collision-induced reactive-complex. Specifically, using nanosecond time-resolved infrared emission spectroscopy, it is revealed that collisions between hyperthermal hydrogen atoms (with 59 kcal/mol of kinetic energy) and ambient SO2 result in the production of vibrationally highly excited SO2 with >14,000 cm −1 of internal energy. The lower limit of the cross-section for this super energy transfer process is determined to be 0.53±0.05Å 2 , i.e., 2% of all hard sphere collisions. This cross-section is orders of magnitude greater than that predicted by the exponential energy gap law, which is commonly used for describing collisional energy transfer through repulsive interactions.

Collisional Energy Transfer from Vibrationally Excited Hydrogen Isocyanide

“…Efficient V-T energy transfer has also been demonstrated for collisional partners capable of forming transient reactive collision complexes. , We have previously demonstrated this mechanism through examining the collisions between hyperthermal hydrogen atoms and HCCH as well as sulfur dioxide (SO 2 ). , It was shown that H atoms prepared with ∼60 kcal/mol of translational energy were able to transfer up to 70% of this energy into the internal degrees of freedom of HCCH with high probability . In general, any excited species capable of attractive interactions with the collisional quencher could form a transient collision complex and may therefore exhibit enhanced energy transfer via IVR prior to eventual dissociation of the complex.…”

Theoretical Study for the Ground Electronic State of the Reaction OH + SO → H + SO2

“…Recently, Ma et al carried out an experimental investigation on the collision ET between H and SO 2 at the translational energy of 59 kcal mol –1 . Interestingly, they obtained large populations of internally hot SO 2 , which could be rationalized according to the formation of the long-lifetime complex . da Silva et al carried out QCT calculations to simulate this ET process on the DMBE PES, and confirmed that the indirect mechanism via the intermediate formation is responsible for the large ET …”

“…The time-resolved infrared emission of the rotationally excited OH produced from reactive collisions between hot H and SO 2 has been reported . In addition, the species SO 2 has been found to be very hot in its vibrational motions after collisions by a hyperthermal H . QCT calculations on the DMBE PES confirmed that those indirect collisions through long-lifetime wells HOSO or HSO 2 are responsible for the highly vibrational excited SO 2 species …”

Quasi-Classical Trajectory Study of NH(3∑–) + NH(3∑–) Reactive Collisions

“…Such a uniform vibrational distribution of product N 2 is related to a statistical distribution, supporting then the fast vibrational energy distribution introduced in a previous paragraph, i.e., even when the four-body complex lifetime is relatively short in the two-step mechanism, it is long enough as to uniformly distribute the vibrational energy. It is worth mentioning that vibrational distributions can be experimentally measured (see, for example, refs and ). In that case, it will eventually support the current theoretical prediction.…”