Energy Transfer in the 2u (1D2) Ion-Pair State of I2 by Inelastic Collisions with Noble Gas Atoms

The temperature dependence of cross sections for 62P1/2 ↔ 62P3/2 mixing in cesium, induced in collisions with CH4, CH3D, CH2D2, CHD3, and CD4 molecules, has been investigated in a series of sensitized fluorescence experiments over a temperature range 290–650 K. The various cross sections which are of the order of 10−15 cm2, and which exceed similar cross sections for cesium–noble gas collisions by 4 – 6 orders of magnitude, exhibit differences in their variation with temperature. This isotope effect in the collision cross sections is interpreted on the basis of a novel semiclassical theory of electronic to rotational energy transfer. The cross section for mixing induced by collisions with CF4, which was determined in a subsidiary experiment, and which is 2–3 times larger than the methane cross sections, does not show comparable behavior with temperature, probably because the energy transfer takes place to closely lying molecular vibrational states.

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Collision-induced electronic energy transfer from v=0 of the E(0g+) ion-pair state in I2: Collisions with I2(X)

The Journal of Chemical Physics ◽

10.1063/1.1391264 ◽

2001 ◽

Vol 115 (9) ◽

pp. 4132-4138 ◽

Cited By ~ 31

Author(s):

Christopher J. Fecko ◽

Miriam A. Freedman ◽

Thomas A. Stephenson

Keyword(s):

Energy Transfer ◽

Electronic Energy ◽

Ion Pair ◽

Electronic Energy Transfer ◽

Pair State

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Ionization characteristics of the Cys-25/His-159 interactive system and of the modulatory group of papain: resolution of ambiguity by electronic perturbation of the quasi-2-mercaptopyridine leaving group in a new pyrimidyl disulphide reactivity probe

Biochemical Journal ◽

10.1042/bj2900289 ◽

1993 ◽

Vol 290 (1) ◽

pp. 289-296 ◽

Cited By ~ 22

Author(s):

G W Mellor ◽

E W Thomas ◽

C M Topham ◽

K Brocklehurst

Keyword(s):

Ph Dependence ◽

Order Rate Constant ◽

Ion Pair ◽

Catalytic Site ◽

Alkaline Media ◽

Interactive System ◽

Data Set ◽

Pka Value ◽

Compound Ii ◽

Pair State

1. A new thiol-specific reactivity probe 4,4′-dipyrimidyl disulphide [compound (VII), m.p. 110 degrees C, pKa of its monohydronated form 0.91] was synthesized and used to resolve the ambiguity of interpretation of the behaviour of papain (EC 3.4.22.2) in alkaline media known to depend to varying extents on two ionizations with pKa values approx. 8.0-8.5 and > or = 9.5 respectively. 2. A new extensive pH-second-order rate constant (k) data set for the reaction of papain with 2-(acetamido)-ethyl 2′-pyridyl disulphide (IV) demonstrated the existence of a striking rate maximum at pH approx. 4, the independence of k around pH 8 and the increase in k with increase in pH across a pKa value of 10.0, behaviour similar to that of other 2-pyridyl disulphides (R-S-S-2-Py) that lack key substrate-like binding sites in R. 3. Although the simplest interpretation of the pKa value of 10.0 assigns it to the formation of (Cys-25)-S-/(His-159)-Im from the ion-pair state of the papain catalytic site, another interpretation may be conceived in which this pKa value is assigned to another group remote from the catalytic site, the state of ionization of which modulates catalytic-site behaviour. This alternative assignment is shown to require compensating effects in the pH region around 8 such that the formation of (Cys-25)-S-/(His-159)-Im across pKa 8.0-8.5 is without net kinetic effect in the reactions of simple 2-pyridyl disulphides such as compound (IV) and 2,2′-dipyridyl disulphide (II). 4. The lower basicity of compound (VII) relative to that of compound (II) (pKa 2.45) was predicted to diminish or abolish the compensation postulated as a possibility in reactions of 2-pyridyl disulphides because of the decreased effectiveness of reaction via a (His-159)-Im+H-assisted transition state. The characteristics of the pH-dependence of the reaction of papain with compound (VII) which are quite different from those for its reaction with compound (II) support both this prediction and the alternative assignment with a value of 8.3 for the pKa of the formation of (Cys-25)-S-/(His-159)-Im. 5. Evidence that the behaviour of papain towards both substrates and some substrate-derived time-dependent inhibitors is determined not only by the loss of the (Cys-25)-S-/(His-159)-Im+H ion-pair state by dehydronation with pKa 8.3 but also by another ionization of pKa approx. 10.0 is briefly discussed.

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Breakdown of energy transfer gap laws revealed by full-dimensional quantum scattering between HF molecules

Nature Communications ◽

10.1038/s41467-019-12691-8 ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 3

Author(s):

Dongzheng Yang ◽

Jing Huang ◽

Xixi Hu ◽

Hua Guo ◽

Daiqian Xie

Keyword(s):

Energy Transfer ◽

Angular Momentum ◽

Vibrational Energy ◽

Energy Gap ◽

Inelastic Collisions ◽

Rate Coefficients ◽

Quantum Scattering ◽

Final States ◽

Energy Gap Law ◽

Quantitative Basis

Abstract Inelastic collisions involving molecular species are key to energy transfer in gaseous environments. They are commonly governed by an energy gap law, which dictates that transitions are dominated by those between initial and final states with roughly the same ro-vibrational energy. Transitions involving rotational inelasticity are often further constrained by the rotational angular momentum. Here, we demonstrate using full-dimensional quantum scattering on an ab initio based global potential energy surface (PES) that HF–HF inelastic collisions do not obey the energy and angular momentum gap laws. Detailed analyses attribute the failure of gap laws to the exceedingly strong intermolecular interaction. On the other hand, vibrational state-resolved rate coefficients are in good agreement with existing experimental results, validating the accuracy of the PES. These new and surprising results are expected to extend our understanding of energy transfer and provide a quantitative basis for numerical simulations of hydrogen fluoride chemical lasers.

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