The current decade has seen illuminating and extensive study of interplay of topological effects such as Renner–Teller and Jahn–Teller (JT) effects in small molecules. Study of such effects in HCNH molecule showed an interesting feature that for slightly bent system, a pair of JT conical interactions (CIs) appear only for certain nonplanar configuration, in contrast to its appearance in CS configuration (molecular plane) for C2H2 +. Moreover, since the feature of appearance of JT-CIs in two 2Σ+ states of HCNH in some bent configuration may be critically associated to the abundance of HNC in interstellar spaces, as advocated recently by Das and Mukhopadhyay (J. Phys. Chem. 117, 8680 (2013)), the interest in such topological studies have remained relevant. In this article we have investigated such topological effects for slightly bent N2H2 + and HBNH+. Interestingly, the appearance of JT-CIs are, for HBNH+, in molecular plane while for N2H2 +, in certain nonplanar configuration, in sharp contrast to the effect in the otherwise similar pair of molecular systems, C2H2 + and HCNH. © 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group.

DEBASIS MUKHOPADHYAY

Chemistry

A DAS

R MONDAL

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Topological effects in low-lying electronic states of linear N2H2 + and HBNH+ associated with onset of bending

Molecular Physics

Abnormal abundance of HNC in interstellar spaces has been the motivation of many experimental as well as theoretical studies of the branching ratio [HNC]/[HCN] in the dissociation of HCNH, right after its formation from electron capture by HCNH+, available in the upper atmosphere. In the present work we were interested in nonadiabatic studies involving the dissociation channel of HCNH leading to the formation of HNC. This study reports for the first time that the conical intersection (CI) between the states 1 2Σ+ and 22Σ+ exists only in some bent geometry (and not in the collinear geometry) where both of these states have A′ symmetry. This finding is important as this CI is crucial in the dissociation of HCNH. We further report that these two states strongly couple with 12Π, the lowest electronic state of collinear HCNH. Hence we construct a three-state Hilbert subspace (HSS), comprising of the states 12Π, 12Σ+, and 2 2Σ+, in a configuration space where these states interact very strongly and the adiabatic-to-diabatic transformation angles (mixing angle) yield meaningful values of topological (Berry) phase. This leads to the construction of the corresponding three-state diabatic potentials. We advocate that these diabatic potentials, considering both the linear as well as bent configurations, nicely elucidate the formation of the HNC molecule by the CH bond dissociation of HCNH molecule. © 2013 American Chemical Society.

Journal of Physical Chemistry A

Study of nonadiabatic effects in low-lying electronic states of HCNH with implication in its dissociation to HCN and HNC

A few years back T. Vértesi et al. (J Phys Chem A 2005, 109, 3476) gave an elegant procedure to derive the adiabatic-to-diabatic transformation angle (ADT-angle) for lowest two states, γ 12, in presence of their interaction with the higher states. In this article, we explicitly solved the coupled differential equations involving the ADT-angles describing the mixing of four interacting states for the first time to get all the ADT-angles, γ ij's (including the γ 12) associated with well-defined topological phases. In application to a suitable configuration space (CS) of a molecular system, we have demonstrated well-defined Berry phases (Berry M. V., R Soc London Ser A 1984, 45, 392) for an isolated system with as many as four strongly interacting states. © 2012 Wiley Periodicals, Inc. Copyright © 2011 Wiley Periodicals, Inc.

International Journal of Quantum Chemistry

The adiabatic-to-diabatic transformation angle and topological phases for strongly interacting states: Solution with four states

Demonstration of onset of Jahn-Teller (JT) intersections, characterized by a topological phase of π, on introduction of bending in the collinear tetra-atomic C 2H 2 + cation, originally a Renner-Teller (RT) system, has raised interest in the study of the generality of this phenomenon. This interest has initiated similar study by shifting one external light atom from the collinear molecular axes of systems such as HCNH and HC 2O. Recent studies have revealed that slightly bent HCNH poses a specialty in this regard and thus demands focused attention. In the present work we performed a combined study using both the potential intersections and the angular nonadiabatic coupling terms (NACTs) and report two new results: (i) The first result is the appearance of the JT conical intersections (ci's) between the two lowest states of a slightly bent HCNH molecule (1 2A′ and 1 2A-3, originated from collinear X 2Π state) only with certain nonplanar configurations, in contrast to its appearance in C S configuration space (molecular plane) for slightly bent C 2H 2 +, HC 2O, or some other tetra-atomics. This is also associated with the first time demonstration of Berry phase for such a single isolated ci for HCNH molecule. (ii) For energetically higher potentials of slightly bent HCNH, the present study reveals the existence of the intersection of the state 1 2A-3 with the state 2 2A′ (originated from the collinear 1 2Σ + state); in contrast to the (1,2) ci this appears in the molecular plane. The search for ci's has been performed by varying the distances of the two H-atoms (designated as H C and H N) from the C-N axis as well as the dihedral angle φ between the two planes (H C,C,N) and (C,N,H N). Existence of these JT ci's results in deterioration of a two-state Hilbert subspace (HSS) model in diabatization, while the proper choice of an n (&gt;2)-state HSS circumvents this problem. © 2012 American Chemical Society.

Jahn-Teller intersections induced by introduction of bending in linear polyatomics: Study with HCNH, a selected molecular system

We perform ab initio calculation using quantum chemistry package (MOLPRO) on the excited states of Na3 cluster and present the adiabatic PESs for the electronic states 22E′ and 12A1′, and the non-adiabatic coupling (NAC) terms among those states. Since the ab initio calculated NAC elements for the states 22E′ and 12 A1′ demonstrate the numerical validity of so called Curl Condition, such states closely form a sub-Hilbert space. For this subspace, we employ the NAC terms to solve the adiabatic-diabatic transformation (ADT) equations to obtain the functional form of the transformation angles and pave the way to construct the continuous and single valued diabatic potential energy surface matrix by exploiting the existing first principle based theoretical means on beyond Born-Oppenheimer treatment. Nuclear dynamics has been carried out on those diabatic surfaces to reproduce the experimental spectrum for system B of Na3 cluster and thereby, to explore the numerical validity of the theoretical development on beyond Born-Oppenheimer approach for adiabatic to diabatic transformation. © 2011 American Institute of Physics.

Fulltext

Journal of Chemical Physics

Ab initio calculations on the excited states of Na3 cluster to explore beyond Born-Oppenheimer theories: Adiabatic to diabatic potential energy surfaces and nuclear dynamics

We perform ab initio calculation using MOLPRO on the 22E ′ and 12A1′ states of Na3 cluster and explore for locating the point of conical intersections (CIs) in the configuration space (CS). The functional form of Non-Adiabatic Coupling Term (NACT) between the 22E′ states indicates the presence of singularity at four points in the CS. While performing Adiabatic-to-Diabatic Transformation (ADT) [Chem. Phys. Lett. 35 (1975) 112] by employing three state NACTs, two diagonal elements of ADT matrix display four sign changes as a signature of four CIs. Moreover, the locations of those CIs are confirmed by Longuet-Higgins' theorem. © 2011 Elsevier B.V. All rights reserved.

Journal	Data powered by TypesetMolecular Physics
Publisher	Data powered by TypesetTaylor and Francis Ltd.
ISSN	0026-8976
Open Access	No