In this study, the molecular geometry, electronic, magnetic, and vibrational spectra of Schiff base ligand with Fe(II) Complexes were simulated by using density functional theory hybrid methods. NMR, UV-Vis, Raman, Infrared Spectroscopic investigations were carried out. The calculated values have been compared with the corresponding experimental results. Molecular orbital properties, descriptors, the mapping molecular electrostatic potential surface (MEP), and nonlinear optical (NLO) properties have been reported for better understanding at the molecular level. Normal modes analysis and their vibrational assignments were searched by using the Scaled Quantum Mechanical Force Field (SQM-FF) method based on total energy distribution (TED).

Trans-urocanic acid (UA) is found in the outer layer of human skin, where -due to its favorable UV absorption properties- it is thought to act as a natural sunscreen protecting DNA from photodamage. In recent decades it has become clear, however, that the cis-isomer produced upon irradiation has immunosuppressive properties, which is the main reason that UA is no longer employed in commercial sunscreen formulations. As a basic chromophore UA is nevertheless an excellent starting point for the development of potentially harmless nature-inspired sunscreens. Key to such efforts is a fundamental understanding of the photochemistry and photophysics of UA on which there are still quite a number of unresolved questions, and how substitutions affect these properties. Here we report on molecular beam studies of (substituted) UA compounds using Resonance Enhanced MultiPhoton Ionization (REMPI) spectroscopic techniques that demonstrate that previous conclusions need to be revised. Together with FT-IR and UV/Vis absorption studies of these compounds in various solvents they provide a comprehensive view on the photoactive properties of these compounds, as well as the influence of the presence of different conformers and tautomers.

Food security is one of the major challenges society is currently facing. One of the approaches to meet this challenge is to use molecular light-to-heat converters to extend the growth season and to allow utilization of geographical locations that are currently not suitable. Cinnamates -chromophores used already in nature as sunscreens against damage by UV radiation - from in this respect an attractive starting point for the development of such ‘molecular heaters’. Here we report molecular beam studies on judiciously substituted cinnamates in which we study their spectroscopy and excited-state dynamics using Resonance Enhanced MultiPhoton Ionization (REMPI) spectroscopic methods focussing in particular on how substitutions affect their photophysics and photochemistry. One particularly interesting aspect of these studies is the use of Velocity Map Imaging (VMI) electron detection which allows us to study in much more detail than before the properties of the initially excited state as well as energy dissipation pathways involving ‘dark’ electronically excited states. In combination with advanced quantum chemical calculations, a comprehensive view is obtained of how photon energy is converted into heat, and how these pathways might be optimized.

The formyl ion () is one of the most abundant ions in molecular clouds and represents an excellent candidate to trace dense molecular gas through the evolutionary stages of the interstellar medium (ISM). For this reason, the accurate rotational rate coefficients of and its isotopes with the most abundant perturbing species in the ISM are crucial in non-local thermal equilibrium (LTE) models and deserve special attention. To this end, many efforts have been made in order to retrieve accurate collisional parameters of interacting with the and colliders as well as for some of its isotopologuesTonolo F., Bizzocchi L., Melosso M., Lique F., Dore L., Barone V., Puzzarini C., 2021, The Journal of Chemical Physics, 155, 234306.^,Denis−Alpizar O., Stoecklin T., Dutrey A., Guilloteau S., 2020, Monthly Notices of the Royal Astronomical Society, 497, 4276. However, in spite of laboratory and observational studies on \ceHC¹⁷O+Plummer G., Herbst E., De Lucia F., 1983, The Astrophysical Journal, 270, L99.^,Dore L., Cazzoli G., Caselli P., 2001, Astronomy & Astrophysics, 368, 712. to the best of our knowledge, an accurate characterization of its collisional parameters has not been carried out yet. Although rarer, the isotope assumes a prominent role to avoid problems due to the optical thickness of the parent species emissions. With the aim of filling this lack, this work reports the first calculations of hyperfine resolved rate coefficients for the excitation of by p- (J=0).
We characterized the potential energy surface of the and collisional system by means of the CCSD(T)-F12a/aug-cc-pVQZ level of theory. The interaction energy has been averaged over five orientations and then fitted as an expansion of angular functions. Finally, state-to-state rate coefficients between the lower hyperfine levels have been computed using recoupling techniques for temperature ranging from 5 to 100 K. Tonolo F., Bizzocchi L., Melosso M., Lique F., Dore L., Barone V., Puzzarini C., 2021, The Journal of Chemical Physics, 155, 234306.\end Denis−Alpizar O., Stoecklin T., Dutrey A., Guilloteau S., 2020, Monthly Notices of the Royal Astronomical Society, 497, 4276..\end Plummer G., Herbst E., De Lucia F., 1983, The Astrophysical Journal, 270, L99. Dore L., Cazzoli G., Caselli P., 2001, Astronomy & Astrophysics, 368, 712.,

The alkaline earth monohalides have a number of applications. They are a continuing focus of ultracold experiments; they provide insight into the calcium ionic bonding of biological relevance; and they are molecular prototypes for Rydberg spectroscopy. In Rydberg spectroscopy, a MQDT model is extremely effective, but not all states are of purely Rydberg type since a lifetime matrix calculated in Serhan Altunata's work describes a shape resonance that couples Σ states to dissociation. To explore this, a wide range of CaF properties have been obtained in a series of UHF-CCSD(T) calculations extending to nearly 40,000 cm-1 above the ground state. Excited states were converged from QRHF initial guesses and extended to include CCSD(T) first-order properties, computed analytically. Remarkably accurate results are obtained for dipole moments known from molecular beam experiments, as well as very good results found for known values of bond length, vibrational frequency and anharmonicity. Several new states are predicted. In general, it is not possible for two states of the same symmetry to be quite close in energy and yet cross unless electronic configurations are very different. The calculation finds that to be the case for two higher ²Σ⁺ states that differ dramatically in electron density and bond length, one with a short bond length and electron density along the axis far away from the center of mass, and a second with a long bond length with density in a ring close to the center of mass. The states have large quadrupole moments of opposite signs. The long bond length state may be related to the predicted shape resonance.

This work presents a generic framework for modeling the energy transfer processes between rovibronic quantum states in diatomic molecules upon laser excitation. A comprehensive set of rate equations (denoted here as the master equation) was developed to describe the interactions between radiation processes (i.e. absorption, stimulated emission and fluorescence), collision processes (including rotational energy transfer, vibrational energy transfer, and electronic quenching), and losses such as inter-system crossing an chemical reactions (including predissociation and ionization). The rate coefficients were fully parameterized using physical quantities such as the transnational temperature of the exited molecule, the energy gap and the start/end quanta across the transfer process, and the numerical expressions of parameterization were guided by a critical review of the existing literature. A stiff ODE solver with adjustable step-size was implemented to accommodate the wide range of physical timescales involved in the master equation. To demonstration the utility of the current modeling approach, simulations were performed for OH and NO molecules excited by selected transitions in the A-X (0,0) and (1,0) bands, and the spectro-temporal features of the predicted fluorescence signals were analyzed and validated against previous experimental results. Additional simulations were also conducted at extreme conditions of ultra-short laser pulses and very high laser energies, which revealed non-monotonic trends resulting from complications of strong non-linearity and spectral-temporal correlation at these conditions, indicating the existence of an optimal pulse length or laser energy (not necessarily the shorter or higher the better) for typical LIF applications. This modeling framework will be released online soon and should prove useful in aiding the design and analysis of modern quantitative LIF measurements.

Hydrogen cyanide (HCN) is extensively studied in combustion and exoplanetary research for its important role in both fields. Laser-based detection of HCN in both fields, among other applications, necessitates quantifying the pressure and temperature dependence of its absorption cross-section. Here, we introduce a method to access HCN’s strongest IR band, ν₂, near 712 cm⁻¹via a high-resolution custom-designed laser source. Difference-frequency generation (DFG) between a cw EC-QCL and a pulsed CO₂ gas laser in an orientation-patterned GaAs crystal is employed to generate laser light in the long-wavelength mid-IR region. The DFG laser can be wavelength-tuned over 667 - 865 cm⁻¹. We employed our DFG laser to quantify the pressure dependence of absorption cross-section of the Q-branch of the ν₂ band of HCN over the range 100 - 800 Torr. Furthermore, we exploited the developed laser source in conjunction with a shock tube to measure the temperature dependence of absorption cross-section of the peak of the Q-branch behind reflected shock waves over the temperature range 850 - 3000 K. We compared our results with HITRAN simulations. Ultimately, we utilized these results in measuring HCN formation time-histories in a reactive environment behind reflected shock waves.

Methods for solving the Schrödinger equation have seen an explosive growth in recent years, as the importance of incorporating quantum effects in numerical simulations in order to obtain experimentally accurate data becomes increasingly recognized. In practical terms, there are just three primary factors that currently limit what can be achieved. These are: (a) SYSTEM SIZE, i.e., the number of degrees of freedom that can be treated explicitly quantum mechanically; (b) NUMERICAL ACCURACY, measured in terms of convergence with respect to ALL POSSIBLE computational parameters such as basis sizes; (c) ENERGY EXCITATION or the total number of accurately computed states. Broadly speaking, current methods can deliver on any two of these goals, but achieving all three at once remains an enormous challenge. In this presentation, we shall describe just such a method, and demonstrate how it can be used to "hit the trifecta" in the context of molecular vibrational spectroscopy calculations.J. Sarka and B. Poirier, J. Chem. Theory Comput. 17, 7732-7744 (2021).n particular, we compute thousands of vibrational states for the 12D acetonitrile molecule (CH₃CN), to a target numerical convergence of a few 10⁻² cm⁻¹ or better. In other words, we compute ALL vibrational states for this six-atom system in full quantum dimensionality, and throughout the entire dynamically relevant spectral range, to near spectroscopic accuracy. To our knowledge, no such vibrational spectroscopy calculation has ever previously been performed-although given the generality of the method, we anticipate there will be many more such calculations to follow.

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J. Sarka and B. Poirier, J. Chem. Theory Comput. 17, 7732-7744 (2021).I

Modern computational techniques used to simulate quantum chemistry are on the boundary of tractability due to the exponential growth of the molecular wavefunction, requiring a careful balance between molecule size and simulation accuracy. In recent years, quantum computing has risen in popularity as a potential alternative to conventional (classical) techniques; however, most methods rely on access to "digital" quantum computers composed of qubits and quantum gates, which at present are severely limited by noise. We have developed a real-time, analog approach to simulate vibronic chemical dynamics with existing quantum technology. Our approach uses an intuitive mapping of molecular electronic and vibrational degrees of freedom onto quantum resonators and qudit (d-level system) states, with controllable couplings between degrees of freedom. The measurement output can be mapped onto different time-dependent observables, including the time-domain simulation of vibronic spectra. Our approach can also incorporate controlled sources of noise to simulate system-bath interactions and dissipative dynamics at a minimal cost. We present experimental results using a trapped-ion device, thus showing the potential for near-term simulation of chemical dynamics in complex environments beyond the abilities of classical computers.

Laser absorption spectroscopy has been proved to be a powerful diagnostic tool for high enthalpic systems like exoplanets, combustion applications and hypersonic flows. But there is a scarcity of high-temperature absorption data, especially for large molecules due to technical challenges like limited availability of optical materials necessary to withstand high temperatures. Furthermore, generating a chemically stable, homogeneous and steady gas state for a sufficient duration to carry out such high-temperature measurements is rather complicated and most experimental approaches satisfy only a few of these requirements. In this work, we present measurements of temperature-dependent absorption cross-section between 950-1190 cm⁻¹of dimethyl ether (DME) and diethyl ether (DEE) and their direct pyrolysis study. The methodology employed here consists of rapid tuning, wide range/fixed wavelength MIRcat-QT laser in conjugation with shock tube. The spectral measurements are performed between 600-900 K, at around 1.2 bar. The measured IR absorption spectra are the first experimental measurements of high-temperature spectra of these species and show strong temperature dependence. For the first time absorption cross-section correlation has been provided for a wide range of spectra over a wide range of temperatures. These measured spectra have provided a significant idea about the trend in spectra at elevated temperatures and helped in the selection of promising wavelengths for sensitive detection. DME and DEE pyrolysis studies are performed at 1121.7 cm⁻¹and 1115 cm⁻¹respectively by providing the marginal temperature dependence absorption cross-section correlations.

l0pt Figure One famous family of chemically recyclable polymers are produced from fused-ring cyclooctene monomers, and their chemical properties are highly tunable by modifying the functional groups from the monomers. The photochemical [2+2] cycloaddition is crucial to synthesizing such a fused-ring cyclooctene monomer, but its mechanistic details remain mysterious. Recently we observed a significant isomerization probability in the photochemical [2+2] cycloaddition between 1,5-cyclooctadiene and maleic anhydride, which produces more trans-fused-ring cyclooctene than the cis counterpart. In the present work, we investigated the photochemical mechanism (figure) of this reaction using density functional theory (DFT), with the aim of decoding when this isomerization happens and how it is correlated to the yields of products. We found that the isomerization occurs only at the first excited state after a charge transfer photoexcitation from 1,5-cyclooctadiene to maleic anhydride, and its activation barrier depends on the structure and orientation of the reactant complex. After the isomerization, the reactant complex barrierlessly reaches a conical intersection (CI) between the ground and the first excited states and quickly passes to the ground state of the product after climbing over an affordable activation barrier. Compared to a cis counterpart, the trans product exhibits a slightly lower total energy and a significantly lower activation barrier, indicating its trans configuration is favorable both thermodynamically and kinetically. Our model has been effectively extended to various functional groups and can be used to guide the rational design of photochemically synthesized fused-ring monomers.