Calculations of quantum tunnelling rates for muonium reactions with methane, ethane and propane

Abstract

<p>Thermal rate constants for Mu + CH₄, Mu + C₂H₆ and Mu + C₃H₈ and their equivalent reactions with H were evaluated with ab initio instanton rate theory. The potential-energy...</p>

Large Anharmonic Effects on Tunneling and Kinetics: Reaction of Propane with Muonium

“…The KIE is defined here as k Mu /k H , where H denotes protium, and a KIE less than unity is called inverse. Theoretical predictions of the rate constants for Mu + H 2 , 36,37,40,[53][54][55][56][57]59,60 Mu + CH 4 , [50][51][52]58,61 and Mu + C 2 H 6 61 reactions agree well with experiment. 38,41,44,45,53,54 In these reactions, the KIEs are inverse and most so at lower temperature.…”

“…Mu reactions provide severe tests of theoretical treatments of quantum effects. 36−60 Therefore, a recent report of a large difference between theory 61 and experiment 62,63 for the rate constant of the Mu + C 3 H 8 reaction is an opportunity to learn if additional physical effects should be included in simulations.…”

Instanton theory of tunneling in molecules with asymmetric isotopic substitutions

“…The standard approach is currently available in i-PI 93 and MOLPRO 94 and can thus be used to study tunnelling in asymmetric systems too with very minor modifications to the code. One could also employ machine-learning techniques as has been done with other instanton approaches 88,95,96 to allow efficient application with ab initio electronicstructure calculations.…”

“…For instance, it can be observed that the H 6 atom is the only one directly involved in the proton transfer process and makes the largest contribution to the tunnelling path. We can quantify this in the same manner as we have done in our previous work 88 This figure also defines our labelling scheme, which follows that used by Baughcum et al 4 uating the squared mass-weighted path length, which is in this case proportional to the action, S. 89 From this, we find that atom 6 contributes about 70% of the total action, whether it is deuterated or not, although the overall path length (and hence the action) does of course increase significantly when a D 6 substitution is introduced. Tunnelling is thus strongly dependent on the isotope of this particular atom, as our results shall demonstrate.…”

Time Evolution of ML-MCTDH Wavefunctions I: Gauge Conditions, Basis Functions, and Singularities

“…[18][19][20][21][22][23][24][25][26] As these approaches can, in principle, be converged to give the exact quantum dynamics, the results obtained using these techniques are also often used to benchmark other approaches. [27][28][29] However, despite these successes there are regimes in which such approaches fail to capture the correct dynamics. [30][31][32] One important cause for such difficulties is that the underlying equations-of-motion (EOMs) can become singular or nearly singular, necessitating the use of regularization techniques.…”