First principles determination of the NH2/ND2($\skew4\tilde A, \skew3\tilde X$Ã,X̃) branching ratios for photodissociation of NH3/ND3 via full-dimensional quantum dynamics based on a new quasi-diabatic representation of coupled <i>ab initio</i> potential energy surfaces

Ma, Jianyi; Zhu, Xiaolei; Guo, Hua; Yarkony, David R.

doi:10.1063/1.4753425

Cited by 46 publications

(60 citation statements)

References 81 publications

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“…The potential energy surface (PES) used in the QCT calculation is from that devised by Zhu and Yarkony (ZY) and their coworkers (Zhu et al 2012) which is a 2x2 quasi-diabatic permutation invariant potential matrix designed for studying the photodissociation of ammonia (NH 3 ) in its first absorption band. Quantum dynamical studies on these PES have achieved excellent agreement with experimental data, validating the PES (Ma et al 2012;Xie et al 2014). Only the lower adiabat, which corresponds to the ground electronic state of NH 3 , was used in our calculations reported here.…”

Section: Theoretical Calculations Of the H + Nh 2 H-exchange Reaction...supporting

confidence: 69%

The ortho-to-para ratio of interstellar NH₂: quasi-classical trajectory calculations and new simulations

Gal

Herbst

Xie

et al. 2016

A&A

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Based on recent Herschel results, the ortho-to-para ratio (OPR) of NH 2 has been measured towards the following high-mass starforming regions: W31C (G10.6-0.4), W49N (G43.2-0.1), W51 (G49.5-0.4), and G34.3+0.1. The OPR at thermal equilibrium ranges from the statistical limit of three at high temperatures to infinity as the temperature tends toward zero, unlike the case of H 2 . Depending on the position observed along the lines-of-sight, the OPR was found to lie either slightly below the high temperature limit of three (in the range 2.2-2.9) or above this limit (∼ 3.5, 4.2, and 5.0). In low temperature interstellar gas, where the H 2 is para-enriched, our nearly pure gas-phase astrochemical models with nuclear-spin chemistry can account for anomalously low observed NH 2 -OPR values. We have tentatively explained OPR values larger than three by assuming that spin thermalization of NH 2 can proceed at least partially by H-atom exchange collisions with atomic hydrogen, thus increasing the OPR with decreasing temperature. In this paper, we present quasi-classical trajectory calculations of the H-exchange reaction NH 2 + H, which show the reaction to proceed without a barrier, confirming that the H-exchange will be efficient in the temperature range of interest. With the inclusion of this process, our models suggest both that OPR values below three arise in regions with temperatures 20 − 25 K, depending on time, and values above three but lower than the thermal limit arise at still lower temperatures.

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Section: Theoretical Calculations Of the H + Nh 2 H-exchange Reaction...supporting

confidence: 69%

The ortho-to-para ratio of interstellar NH₂: quasi-classical trajectory calculations and new simulations

Gal

Herbst

Xie

et al. 2016

A&A

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“…As a consequence, the corresponding relative propensity of NH 2 (A ˜) of B6% must be considered as a lower limit for the 2 3 0 excitation. The branching ratio found for the 2 4 0 transition is somewhat larger than that estimated by Ashfold and co-workers 18 and recent theoretical calculations by Ma et al 19 Despite the amount of literature related to the photodissociation dynamics of the NH 3 A ˜' X ˜system, little work has been devoted to the study of the dissociation anisotropy. Ashfold and coworkers have published the single detailed analysis up to date, in which the anisotropy parameter b was extracted from the NH 2 (n 2 , N, K a ) populations for the 0 0 0 and 2 1 0 transitions.…”

Section: Resultsmentioning

confidence: 58%

A velocity map imaging study of the photodissociation of the Ã state of ammonia

Rodríguez

González

Rubio-Lago

et al. 2014

Phys. Chem. Chem. Phys.

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NH3(Ã) photodissociation dynamics has been studied using a combination of velocity map imaging (VMI) and resonance-enhanced multiphoton ionization (REMPI) of the H-atom product. H(+) ion images have been recorded after excitation to the first five NH3 (Ã, ν2' = n) ← (X, ν = 0) vibronic transitions (denoted as 0(0)(0) and 2(0)(n) with n = 1-4). The measured high-resolution H-atom kinetic energy distributions (KED) show a dense set of sharp structures related to rovibrational states of the NH2 co-fragment. A careful simulation of the KEDs in terms of the known internal energies of the NH2 fragment has allowed the extraction of the non-adiabatic NH2(X) rovibrational populations for the 0(0)(0), 2(0)(1) and 2(0)(2) transitions, which are in good agreement with previous measurements. For the 2(0)(3) and 2(0)(4) transitions, some features of the KED have been assigned to rovibrational states of NH2(Ã) fragments produced adiabatically. In particular, the sharp feature distinctively observed at very low kinetic energies in the H-atom KED for the 2(0)(4) transition has been undoubtedly assigned to H atoms produced in correlation with rotationally excited NH2 fragments in the Ã electronic state. For these two transitions, the analysis of the KEDs has allowed the determination of the NH2(X, Ã) rovibrational populations and precise electronic branching ratios, Φ* = [NH2(Ã)]/([NH2(X)] + [NH2(Ã)]). A speed-dependent anisotropy analysis of the H-atom images has been made for all transitions, which provides a picture of the partitioning of the available energy among the NH2 co-product internal modes - including the electronic branching ratios - in terms of a roaming-like mechanism.

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“…This method has been applied to represent a diabatic Hamiltonian only very recently. [44][45][46] A very recent modification of the method by Bowman and Braams 43 is the use of neural networks in connection with CNP invariant polynomials but so far this method is limited to single adiabatic PESs. 47,48 Another possibility is the double manybody expansion by Varandas and co-workers.…”

Section: Introductionmentioning

confidence: 99%

Full-dimensional diabatic potential energy surfaces including dissociation: The 2E″ state of NO3

Eisfeld

Vieuxmaire

Viel

2014

The Journal of Chemical Physics

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A scheme to produce accurate full-dimensional coupled diabatic potential energy surfaces including dissociative regions and suitable for dynamical calculations is proposed. The scheme is successfully applied to model the two-sheeted surface of the (2)E″ state of the NO3 radical. An accurate potential energy surface for the NO₃⁻ anion ground state is developed as well. Both surfaces are based on high-level ab initio calculations. The model consists of a diabatic potential matrix, which is expanded to higher order in terms of symmetry polynomials of symmetry coordinates. The choice of coordinates is key for the accuracy of the obtained potential energy surfaces and is discussed in detail. A second central aspect is the generation of reference data to fit the expansion coefficients of the model for which a stochastic approach is proposed. A third ingredient is a new and simple scheme to handle problematic regions of the potential energy surfaces, resulting from the massive undersampling by the reference data unavoidable for high-dimensional problems. The final analytical diabatic surfaces are used to compute the lowest vibrational levels of NO₃⁻ and the photo-electron detachment spectrum of NO₃⁻ leading to the neutral radical in the (2)E″ state by full dimensional multi-surface wave-packet propagation for NO3 performed using the Multi-Configuration Time Dependent Hartree method. The achieved agreement of the simulations with available experimental data demonstrates the power of the proposed scheme and the high quality of the obtained potential energy surfaces.

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First principles determination of the NH2/ND2($\skew4\tilde A, \skew3\tilde X$Ã,X̃) branching ratios for photodissociation of NH3/ND3 via full-dimensional quantum dynamics based on a new quasi-diabatic representation of coupled ab initio potential energy surfaces

Cited by 46 publications

References 81 publications

The ortho-to-para ratio of interstellar NH₂: quasi-classical trajectory calculations and new simulations

The ortho-to-para ratio of interstellar NH₂: quasi-classical trajectory calculations and new simulations

A velocity map imaging study of the photodissociation of the Ã state of ammonia

Full-dimensional diabatic potential energy surfaces including dissociation: The 2E″ state of NO3

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First principles determination of the NH2/ND2($\skew4\tilde A, \skew3\tilde X$Ã,X̃) branching ratios for photodissociation of NH3/ND3 via full-dimensional quantum dynamics based on a new quasi-diabatic representation of coupled ab initio potential energy surfaces

Cited by 46 publications

References 81 publications

The ortho-to-para ratio of interstellar NH2: quasi-classical trajectory calculations and new simulations

The ortho-to-para ratio of interstellar NH2: quasi-classical trajectory calculations and new simulations

A velocity map imaging study of the photodissociation of the Ã state of ammonia

Full-dimensional diabatic potential energy surfaces including dissociation: The 2E″ state of NO3

Contact Info

Product

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The ortho-to-para ratio of interstellar NH₂: quasi-classical trajectory calculations and new simulations

The ortho-to-para ratio of interstellar NH₂: quasi-classical trajectory calculations and new simulations