Dipole moment and polarizability differences between NH3 and ND3

Halevi, E. Amitai; Haran, E N; Ravid, B.

doi:10.1016/0009-2614(67)85079-6

Cited by 8 publications

(1 citation statement)

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“…Calculations performed using ADO theory predict that the reaction rate constants for the two isotopologues should be very similar, with a small normal KIE of k H =k D ¼ 1:1 anticipated (see Table 1). This small difference in the expected rate constants arises from differences in the polarisability and dipole moment of the isotopologues [26][27][28] , in addition to their different masses. Not only is the magnitude of the predicted ADO rate constants larger than in our measurements (see Fig.…”

Section: Resultsmentioning

confidence: 99%

Strong inverse kinetic isotope effect observed in ammonia charge exchange reactions

et al. 2020

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Isotopic substitution has long been used to understand the detailed mechanisms of chemical reactions; normally the substitution of hydrogen by deuterium leads to a slower reaction. Here, we report our findings on the charge transfer collisions of cold Xe þ ions and two isotopologues of ammonia, NH 3 and ND 3. Deuterated ammonia is found to react more than three times faster than hydrogenated ammonia. Classical capture models are unable to account for this pronounced inverse kinetic isotope effect. Moreover, detailed ab initio calculations cannot identify any (energetically accessible) crossing points between the reactant and product potential energy surfaces, indicating that electron transfer is likely to be slow. The higher reactivity of ND 3 is attributed to the greater density of states (and therefore lifetime) of the deuterated reaction complex compared to the hydrogenated system. Our observations could provide valuable insight into possible mechanisms contributing to deuterium fractionation in the interstellar medium.

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Section: Resultsmentioning

confidence: 99%

Strong inverse kinetic isotope effect observed in ammonia charge exchange reactions

et al. 2020

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Polarization differences between isotopic molecules

Halevi

2009

Int. J. Quantum Chem.

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This paper constitutes a brief report on the determination of dipole moment differences by a differential dielectric constant method. The results are sufficiently precise to be compared with the corresponding differences obtained with modern spectroscopic techniques. It is shown that the two sets of results are concordant if-and only if-Van Vleck's equation for electric polarization is used.Over forty years have elapsed since Van Vleck [l, 21 derived the classical Debye equation for electric polarization from quantum mechanical principles. Debye's familiar equation for a dilute polar gas is:The total molar polarization P is conventionally separated into the temperatureindependent "distortion polarization" PE+A and the "orientation polarization" POR, which is linear in the reciprocal temperature. It expresses the inherently macroscopic quantity, P, determined by the bulk dielectric constant E and the molar volume Pin terms of the mean molecular polarizability a and the molecular dipole moment p.Van Vleck confirmed Equation (1) for the quantum-mechanical rotating oscillator, for which ,u is no longer the fixed dipole moment of a rigid rotator but poo, the expectation value for the lowest vibrational level (ui = 0 for all i) of the non-rotating molecule (J = 0). He also showed that, if rotational quantization is taken into account, a third term must be added to Equation (1

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Secondary equilibrium isotope effects on acidity

Perrin

2010

Advances in Physical Organic Chemistry

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Dipole moment and polarizability differences between NH3 and ND3

Cited by 8 publications

References 8 publications

Strong inverse kinetic isotope effect observed in ammonia charge exchange reactions

Strong inverse kinetic isotope effect observed in ammonia charge exchange reactions

Polarization differences between isotopic molecules

Secondary equilibrium isotope effects on acidity

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