Resonance Theory of Termolecular Recombination Kinetics: H+H+M→H2M

Roberts, Robert E.; Bernstein, R. B.; Curtiss, C. F.

doi:10.1063/1.1671032

Cited by 155 publications

(57 citation statements)

References 74 publications

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“…Note that the resonances with very large lifetimes are not expected to be in equilibrium, since they do not form or decay quickly enough to maintain a steady-state requirement. 58 This may not be the case for the decay rates of the HN 2 resonances, which are very short-lived. On the other hand, resonances with very short lifetimes are difficult to distinguish from the so-called nonresonant contributions.…”

Section: ∆F(e)mentioning

confidence: 99%

“…On the other hand, resonances with very short lifetimes are difficult to distinguish from the so-called nonresonant contributions. 58,59 Thus, our estimated equilibrium constant is likely to underestimates the true one. Using the sum-overstates model with the assumption 57 that the resonances are J-independent leads to the same rate constants within the indicated significant figures.…”

Section: ∆F(e)mentioning

confidence: 99%

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Unimolecular and Bimolecular Calculations for HN₂

et al. 2005

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Section: ∆F(e)mentioning

confidence: 99%

Section: ∆F(e)mentioning

confidence: 99%

Unimolecular and Bimolecular Calculations for HN₂

et al. 2005

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“…We have come back up to L-= 8 ; and that this difference shown (12) [9] that whence the total rate of dissociation of H, would be which identifies the overall rate constant for dissociation with rotational equilibration as Table 3 is always greater with t~~nnelling than without, although sometimes the difference is insignificant as some of the lifetimes of quasi-bound levels with respect to predissociation are extremely long (18,21); the first really significant difference occurs at J = 30. Third, if rotational equilibration is assumed, and if thcrc were no tunnelling, there would be a significant contribution to the dissociation from all rotational states, with J = 0 and J = 38 being among the weakest contributors, the former because of its unfavorable statistical weight (2J + 1 = I), and the latter because, despite its high statistical weight (2J + 1 = 77), the energy requirement is too high (the contributions from odd states of high J are about three times as large as for even J as expected).…”

Section: Dissociation Of the J = 21 State Of Hmentioning

confidence: 99%

“…severely depleted: the depletion however is a much more severe f~~n c t i o n of J than of v. Table 5 compares for para-M, (even J) and for ortho-H, (odd J) the rate constants for dissociation from 1500 to 5000 OK, caiculated according to [16], [17], and [18], both with and without tunnelling. It is obvious immediately that the inclusion of tunnelling from the predissociating levels makes only a negligible difference in this temperature range, this being particularly the case at high temperatures.…”

Section: Dissociation Of the J = 21 State Of Hmentioning

confidence: 99%

The Master Equation for the Dissociation of a Dilute Diatomic Gas. VIII. The Rotational Contribution to Dissociation and Recombination

Ashton¹,

McElwain²,

Pritchard³

1973

Can. J. Chem.

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The dissociation of the J = 21 state of H,, and the recombination of atoms into that state, have been examined in detail. The J = 21 state of H, has two quasi-bound levels, one long-lived and the other short-lived, but the rate constants for dissociation or recombination involving this state are almost completely independent of the tunnelling rates into and out of the quasi-bound levels, and are in fact determined by bottleneck effects occurring lower down the vibrational ladder. Direct integration of the relaxation equations shows that, either excluding or including tunnelling, the dissociation and recombination rate constants obey the rate-quotient law, and that in the latter case the lowest eigenvalue of the relaxation matrix properly reflects the pressure dependence of the dissociation rate constant. Less extensive examination of the dissociation properties of other rotational states indicates that these conclusions are general, except that there is no strong bottleneck effect for very high rotational states (J > 30).It is shown that if full rotational equilibration is assumed, the sum, weighted over all J, of theindividual dissociation rate constants leads to an overall dissociation rate constant which is much too high, suggesting strongly that rotational equilibration cannot occur amongst the very high J states.A factored form of the master equation is then examined in which either only T-V or only T-R processes take place, over the temperature range 1500-5000 OK. It is found that in this approximation the upper rotational states are very strongly depleted, and that the Arrhenius temperature coefficients of the dissociation rate constants are between 92 and 94 kcal mol-', depending upon :he choice of rotational transition probabilities. The calculation suggests that one contributory cause of "low activation energies" in dissociation reactions is strong rotational depopulation of the very high rotational states, and its importance in relation to other possible causes is discussed.The smallest eigenvalues of the 177th order matrix representing the dissociation of para-H, and of the 172nd order matrix representing the dissociation of ortho-H, confirm that the factored model gives an acceptable representation of the dissociation rate of H z in this temperature range; hence the conclusions of the factored model in respect of strong rotational depopulation are probably valid. Finally, it is shown that the second smallest eigenvalue of the full relaxation matrix changes by a factor of three a t 1500 "K or by a factor of ten at 5000 "K when only rotational transition probabilities are varied, thus identifying the relaxation which immediately precedes the dissociation reaction in a shock wave as a T-VR rather than a T-V relaxation.An exploratory series of calculations for deuterium was carried out for the range of temperatures 700-5000 "K, using the latter model which includes full coupling between rotation, vibration, and dissociation, i.e., using matrices of order 348 and 355 for ortho-and para-deuterium, respect...

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“…To calculate the formation rate of ground-state Ag 3 He pairs, we apply the resonant three-body recombination model developed by Roberts, Bernstein, and Curtiss (RBC) 85 (also known as the Lindemann recombination mechanism). Under this † The Ag- 3 He rate varies only slightly with field.…”

Section: Molecular Formationmentioning

confidence: 99%

Formation and dynamics of van der Waals molecules in buffer-gas traps

Brahms

Tscherbul

Zhang

et al. 2011

Phys. Chem. Chem. Phys.

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We show that weakly bound He-containing van der Waals molecules can be produced and magnetically trapped in buffer-gas cooling experiments, and provide a general model for the formation and dynamics of these molecules. Our analysis shows that, at typical experimental parameters, thermodynamics favors the formation of van der Waals complexes composed of a helium atom bound to most open-shell atoms and molecules, and that complex formation occurs quickly enough to ensure chemical equilibrium. For molecular pairs composed of a He atom and an S-state atom, the molecular spin is stable during formation, dissociation, and collisions, and thus these molecules can be magnetically trapped. Collisional spin relaxations are too slow to affect trap lifetimes. However, 3 He-containing complexes can change spin due to adiabatic crossings between trapped and untrapped Zeeman states, mediated by the anisotropic hyperfine interaction, causing trap loss. We provide a detailed model for Ag 3 He molecules, using ab initio calculation of Ag-He interaction potentials and spin interactions, quantum scattering theory, and direct Monte Carlo simulations to describe formation and spin relaxation in this system. The calculated rate of spin-change agrees quantitatively with experimental observations, providing indirect evidence for molecular formation in buffer-gas-cooled magnetic traps.The ability to cool and trap molecules holds great promise for new discoveries in chemistry and physics [1][2][3][4] . Cooled and trapped molecules yield long interaction times, allowing for precision measurements of molecular structure and interactions, tests of fundamental physics 5,6 , and applications in quantum information science 7 . Chemistry shows fundamentally different behavior for cold molecules 8 , and can be highly controlled based on the kinetic energy, external fields 9 , and quantum states 10 of the reactants.Experiments with cold molecules have thus far involved two classes of molecules: Feshbach molecules and deeply bound ground-state molecules. Feshbach molecules are highly vibrationally excited molecules, bound near dissociation, which interact only weakly at long range, due to small dipole moments. They are created by binding pairs of ultracold atoms using laser light (photoassociation), ac magnetic fields (rf as- . By contrast, ground-state heteronuclear molecules often have substantial dipole moments and are immune to spontaneous decay and vibrational relaxation, making these molecules more promising for applications in quantum information processing 7 and quantum simulation 11 . These molecules are either cooled from high temperatures using techniques such as buffer-gas cooling or Stark deceleration, or are created via coherent deexcitation of Feshbach molecules.This article introduces a third family to the hierarchy of trappable molecules -van der Waals (vdW) complexes. VdW molecules are bound solely by long-range dispersion interactions, leading to the weakest binding energies of any groundstate molecules, on the order of a wavenum...

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Resonance Theory of Termolecular Recombination Kinetics: H+H+M→H2M

Cited by 155 publications

References 74 publications

Unimolecular and Bimolecular Calculations for HN₂

Unimolecular and Bimolecular Calculations for HN₂

The Master Equation for the Dissociation of a Dilute Diatomic Gas. VIII. The Rotational Contribution to Dissociation and Recombination

Formation and dynamics of van der Waals molecules in buffer-gas traps

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Resonance Theory of Termolecular Recombination Kinetics: H+H+M→H2M

Cited by 155 publications

References 74 publications

Unimolecular and Bimolecular Calculations for HN2

Unimolecular and Bimolecular Calculations for HN2

The Master Equation for the Dissociation of a Dilute Diatomic Gas. VIII. The Rotational Contribution to Dissociation and Recombination

Formation and dynamics of van der Waals molecules in buffer-gas traps

Contact Info

Product

Resources

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Unimolecular and Bimolecular Calculations for HN₂

Unimolecular and Bimolecular Calculations for HN₂