The role of solar photolysis in the atmospheric removal of methacrolein oxide and the methacrolein oxide-water van-der Waals complex in pristine environments.

Biogenic hydrocarbons are emitted into the Earth's atmosphere by terrestrial vegetation as by-products of photosynthesis. Isoprene is one such hydrocarbon and is the second most abundant volatile organic compound emitted into the atmosphere (after methane). Reaction with ozone represents an important atmospheric sink for isoprene removal, forming carbonyl oxides (Criegee intermediates) with extended conjugation.

Ab initio Modeling of Hydrogen Bonding of Remdesivir and Adenosine with Uridine.

Remdesivir (RDV) emerged as an effective drug against the SARS-CoV-2 virus pandemic. One of the crucial steps in the mechanism of action of RDV is its incorporation into the growing RNA strand. RDV, an adenosine analogue, forms Watson-Crick (WC) type hydrogen bonds with uridine in the complementary strand and the strength of this interaction will control efficacy of RDV.

Beyond Born-Oppenheimer Constructed Diabatic Potential Energy Surfaces for HeH.

First-principles based beyond Born-Oppenheimer theory has been employed to construct multistate global Potential-Energy Surfaces (PESs) for the HeH system by explicitly incorporating the Nonadiabatic Coupling Terms (NACTs). Adiabatic PESs and NACTs for the lowest four electronic states (1A', 2A', 3A' and 4A') are evaluated as functions of hyperangles for a grid of fixed values of the hyperradius in hyperspherical coordinates. Conical intersection between different states are validated by integrating the NACTs along appropriately chosen contours.

Construction of Beyond Born-Oppenheimer Based Diabatic Surfaces and Generation of Photoabsorption Spectra: The Touchstone Pyrazine (C N H ).

We construct theoretically "exact" and numerically "accurate" Beyond Born-Oppenheimer (BBO) based diabatic potential energy surfaces (PESs) of pyrazine (C N H ) molecule involving lowest four excited adiabatic PESs (S to S ) and nonadiabatic coupling terms (NACTs) among those surfaces as functions of nonadiabatically active normal modes (Q , Q , Q and Q ) to compute its photoabsorption (PA) spectra. Those adiabatic PESs are calculated using CASSCF as well as MRCI based methodologies, where NACTs are obtained from CP-MCSCF approach. Employing ab initio quantities (adiabatic PESs and NACTs), it is possible to depict the conical intersections (CIs) and develop matrices of diabatic PESs over six normal mode planes.

Jahn-Teller Effect in Orthorhombic Manganites: Hamiltonian and Roto-vibrational Spectrum.

For the first time, using three different electronic structure methodologies, namely, CASSCF, RS2c, and MRCI(SD), we construct adiabatic potential energy surfaces (APESs) and nonadiabatic coupling term (NACT) of two electronic states () of MnO unit, where eight such units share one La atom in LaMnO crystal. While fitting those APESs with analytic functions of normal modes (, ), an empirical scaling factor is introduced considering the mass ratio of eight MnO units with and without one La atom to explore the environmental (mass) effect on MnO unit. When the roto-vibrational levels of MnO Hamiltonian are calculated, peak positions computed from constructed excited APESs are found to be enough close with the experimental satellite transitions [ 2016, 122, 890-901] endorsing our earlier model results [ 2019, 150, 064703].

Photochemistry of 3,6-Didehydropyridazine Biradical─An Untraceable Benzyne Analogue.

We report matrix isolation infrared spectroscopic studies to characterize 3,6-didehydropyridazine , a heterocyclic analogue of benzyne, combined with computations. In this regard, we have utilized 3,6-diiodopyridazine as a photolytic precursor. The experiments toward the generation of the biradical are carried out in argon and nitrogen matrices at 4 K.

Beyond Born-Oppenheimer based diabatic surfaces of 1,3,5-CHF to generate the photoelectron spectra using time-dependent discrete variable representation approach.

In this article, Beyond Born-Oppenheimer (BBO) treatment is implemented to construct diabatic potential energy surfaces (PESs) of 1,3,5-CHF over a series [eighteen (18)] of two-dimensional (2D) nuclear planes constituted with eleven normal modes (, , , , , , , , , and ) to include all possible nonadiabatic interactions among six coupled electronic states (X̃E'', , B̃E' and ). We had formulated explicit expressions of adiabatic to diabatic transformation (ADT) equations [S. Mukherjee, J.

A beyond Born-Oppenheimer treatment of CH radical cation for diabatic surfaces: Photoelectron spectra of its neutral analog using time-dependent discrete variable representation.

We employ theoretically "exact" and numerically "accurate" Beyond Born-Oppenheimer (BBO) treatment to construct diabatic potential energy surfaces (PESs) of the benzene radical cation (CH ) for the first time and explore the workability of the time-dependent discrete variable representation (TDDVR) method for carrying out dynamical calculations to evaluate the photoelectron (PE) spectra of its neutral analog. Ab initio adiabatic PESs and nonadiabatic coupling terms are computed over a series of pairwise normal modes, which exhibit rich nonadiabatic interactions starting from Jahn-Teller interactions and accidental conical intersections/seams to pseudo Jahn-Teller couplings. Once the electronic structure calculation is completed on the low-lying five doublet electronic states (X̃E, B̃E, and C̃A) of the cationic species, diabatization is carried out employing the adiabatic-to-diabatic transformation (ADT) equations for the five-state sub-Hilbert space to compute highly accurate ADT angles, and thereby, single-valued, smooth, symmetric, and continuous diabatic PESs and couplings are constructed.

The role of electron-nuclear coupling on multi-state photoelectron spectra, scattering processes and phase transitions.

We present first principle based beyond Born-Oppenheimer (BBO) theory and its applications on various models as well as realistic spectroscopic and scattering processes, where the Jahn-Teller (JT) theory is brought in conjunction with the BBO approach on the phase transition of lanthanide complexes. Over one and half decades, our development of BBO theory is demonstrated with ab initio calculations on representative molecules of spectroscopic interest (NO2 radical, Na3 and K3 clusters, NO3 radical, C6H6+ and 1,3,5-C6H3F3+ radical cations) as well as triatomic reactive scattering processes (H+ + H2 and F + H2). Such an approach exhibits the effect of JT, Renner-Teller (RT) and pseudo Jahn-Teller (PJT) type of interactions.

Beyond Born-Oppenheimer constructed diabatic potential energy surfaces for F + H reaction.

First principles based beyond Born-Oppenheimer theory has been implemented on the F + H system for constructing multistate global diabatic Potential Energy Surfaces (PESs) through the incorporation of Nonadiabatic Coupling Terms (NACTs) explicitly. The spin-orbit (SO) coupling effect on the collision process of the F + H reaction has been included as a perturbation to the non-relativistic electronic Hamiltonian. Adiabatic PESs and NACTs for the lowest three electronic states (1A', 2A', and 1A″) are determined in hyperspherical coordinates as functions of hyperangles for a grid of fixed values of the hyperradius.

ADT: A Generalized Algorithm and Program for Beyond Born-Oppenheimer Equations of "" Dimensional Sub-Hilbert Space.

The major bottleneck of first principle based beyond Born-Oppenheimer (BBO) treatment originates from large number and complicated expressions of adiabatic to diabatic transformation (ADT) equations for higher dimensional sub-Hilbert spaces. In order to overcome such shortcoming, we develop a generalized algorithm, "ADT" to generate the nonadiabatic equations through symbolic manipulation and to construct highly accurate diabatic surfaces for molecular processes involving excited electronic states. It is noteworthy to mention that the nonadiabatic coupling terms (NACTs) often become singular (removable) at degenerate point(s) or along a seam in the nuclear configuration space (CS) and thereby, a unitary transformation is required to convert the kinetically coupled (adiabatic) Hamiltonian to a potentially (diabatic) one to avoid such singularity(ies).

Aluminum containing molecular bowls and pyridinophanes: use of pyridine modules to access different molecular topologies.

Molecular topologies varying from simple complexes to pyridinophanes (neutral and cationic) and to bicyclic pyridinophane containing organoaluminum (Al-Me) species were synthesized by varying the relative stoichiometry of bis(trimethylsilyl)-N,N'-2,6-diaminopyridine (bap) and the reactive partner (AlMe). The ultimate goal of these reactions was to systematically design cyclic structures containing group 13 elements. To highlight the reaction potential of these shapes, the bowl-shaped pyridinophane was reacted with the Lewis acid, B(CF), to generate a stable cationic derivative.

Electronically Unsaturated Three-Coordinate Aluminum Hydride and Organoaluminum Cations.

New three-coordinate and electronically unsaturated aluminum hydride [LAlH] [HB(C F ) ] (LH=[{(2,6-iPr C H N)P(Ph )} N]H) and aluminum methyl [LAlMe] [MeB(C F ) ] cations have been prepared. The quantitative estimation of Lewis acidity by Gutmann-Beckett method revealed [LAlH] [HB(C F ) ] to be better Lewis acid than B(C F ) and AlCl making these compounds ideal catalysts for Lewis acid-mediated reactions. To highlight that the work is of fundamental importance, catalytic hydroboration of aliphatic and aromatic aldehydes and ketones have been demonstrated.

Two Different Pathways in the Reduction of [(S=)PCl(μ-NtBu)]2 with Na.

Reduction of the cyclodiphosphazane [(S=)ClP(μ-NtBu)]2 (1) with sodium metal in refluxing toluene proceeds via two different pathways. One is a Wurtz-type pathway involving elimination of NaCl from 1 followed by head-to-tail cyclization to give the hexameric macrocycle [(μ-S)P(μ-NtBu)2 P(=S)]6 (2). The other pathway involves reduction of the P=S bonds of 1 to generate colorless singlet biradicaloid dianion trans-[S-P(Cl)(μ-NtBu)]2 (2-) , which is observed in the polymeric structures of three-dimensional [{(S-)ClP(μ-NtBu)2 PCl(S)}Na(Na⋅THF2 )]n (3) and two dimensional [{(S-)ClP(μ-NtBu)2 PCl(S)} (Na⋅THF)2 ]n (4).

Reactivity of a dihydroboron species: synthesis of a hydroborenium complex and an expedient entry into stable thioxo- and selenoxo-boranes.

The reaction of a recently synthesized dihydroboron species complexed with bis(phosphinimino)amide, LBH2 (), (L = [N(Ph2PN(2,4,6-Me3C6H2))2](-)) with 3 equivalents of BH2Cl·SMe2 or one equivalent of BCl3 affords the first stable monohydridoborenium ion, [LBH](+)[HBCl3](-) () that is stable without a weakly coordinating bulky anion. Compound can also be prepared directly by refluxing LH with 3 equivalents of BH2Cl·SMe2. Interestingly, reaction of LBH2 () with elemental sulfur and selenium involves oxidative addition of S and Se into B-H bonds and subsequent release of H2S (or H2Se) from the intermediate LB(SH)2 (or LB(SeH)2) species forming stable compounds with terminal boron-chalcogen double bonds LB[double bond, length as m-dash]S () and LB[double bond, length as m-dash]Se ().