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Special Issue "Insights in Chemistry and Spectroscopy of Excited Electronic States from Theoretical Calculations"

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Department of Chemistry and Biochemistry, Auburn University, Auburn, AL 36849, USA
Interests: quantum chemical calculations; excited electronic states; transition metal chemistry; diffuse electrons; weakly bound molecular complexes; molecular catalysis; solvated electrons

Special Issue Information

Dear Colleagues,

The excited electronic states of molecules and materials play a major role in chemistry and physics. Light-matter interactions observed in the various spectroscopic techniques (electronic spectroscopy, photo-electron spectroscopy and others) are a direct demonstration of accessing excited electronic states. Promoting molecular species or materials to their excited electronic states opens up often reaction channels unavailable in the ground state. Astrophysics, atmospheric chemistry, and photo-catalysis are some areas involving heavily chemistry of excited electronic states. A more subtle importance of excited states is that even “ground-state” chemistry is often driven by excited states via crossings between the potential energy surface of the ground and excited states. Moreover, the involvement of excited states of atoms can explain the formation of exotic chemical bonds. The theory is nowadays a sine-qua-non companion of experiments making possible the explanation of the experimental observations and suggesting directions for future experimental work. Due to the continuous development of quantum chemical methods, the improvement of the capabilities of the supercomputer, but also the difficulties encountered in increasingly more complex experiments, the theory is turning to the protagonist. This issue aspires to be a showcase of this trend.

Dr. Evangelos Miliordos
Guest Editor

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Keywords

excited electronic states
chemical reactions
spectroscopy
light-matter interactions
density functional theory
ab initio calculations
molecular systems
materials

Published Papers (2 papers)

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Research

Open AccessArticle

Shaped Microwave Field in a Three-Level Closed Loop Dense Atomic System

Nadia Boutabba

and

Hazrat Ali

Molecules 2023, 28(5), 2096; https://doi.org/10.3390/molecules28052096 - 23 Feb 2023

Viewed by 513

Abstract

In this work, we investigate the atomic properties of a three-level system under the effect of a shaped microwave field. The system is simultaneously driven by a powerful laser pulse and a weak constant probe that drives the ground state to an upper level. Meanwhile, an external microwave field drives the upper state to the middle transition with shaped waveforms. Hence, two situations are considered: one in which the atomic system is controlled by a strong laser pump and a classical constant microwave field, and another in which both the microwave and pump laser fields are shaped. Finally, for sake of comparison, we investigate the tanh-hyperbolic, the Gaussian and the power of the exponential microwave form in the system. Our results reveal that shaping the external microwave field has a significant impact on the absorption and dispersion coefficient dynamics. In comparison with the classical scenario, where usually the strong pump laser is considered to have a major role in controlling the absorption spectrum, we show that shaping the microwave field leads to distinct results. Full article

(This article belongs to the Special Issue Insights in Chemistry and Spectroscopy of Excited Electronic States from Theoretical Calculations)

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Figure 1

Open AccessArticle

Complete, Theoretical Rovibronic Spectral Characterization of the Carbon Monoxide, Water, and Formaldehyde Cations

Megan C. Davis

Xinchuan Huang

and

Ryan C. Fortenberry

Molecules 2023, 28(4), 1782; https://doi.org/10.3390/molecules28041782 - 13 Feb 2023

Viewed by 1000

Abstract

New high-level ab initio quartic force field (QFF) methods are explored which provide spectroscopic data for the electronically excited states of the carbon monoxide, water, and formaldehyde cations, sentinel species for expanded, recent cometary spectral analysis. QFFs based on equation-of-motion ionization potential (EOM-IP) [...] Read more.

\tilde{A}

^{2}

_{1}

and

\tilde{B}

^{2}

_{1}

states of the formaldehyde cation; only three of these frequencies have experimental assignment available. Rotational constants corresponding to these vibrational excitations are also provided for the first time for all electronically excited states of both of these molecules. EOM-IP-CCSDT/CcC computations support tentative re-assignment of the

ν_{1}

and

ν_{3}

frequencies of the

\tilde{B}

^{2} B_{2}

state of the water cation to approximately 2409.3 cm

^{- 1}

and 1785.7 cm

^{- 1}

, respectively, due to significant disagreement between experimental assignment and all levels of theory computed herein, as well as work by previous authors. The EOM-IP-CCSDT/CcC QFF achieves agreement to within 12 cm

^{- 1}

for the fundamental vibrational frequencies of the electronic ground state of the water cation compared to experimental values and to the high-level theoretical benchmarks for variationally-accessible states. Less costly EOM-IP based approaches are also explored using approximate triples coupled cluster methods, as well as electronically excited state QFFs based on EOM-CC3 and the previous (T)+EOM approach. The novel data, including vibrationally corrected rotational constants for all states studied herein, provided by these computations should be useful in clarifying comet evolution or other remote sensing applications in addition to fundamental spectroscopy. Full article

(This article belongs to the Special Issue Insights in Chemistry and Spectroscopy of Excited Electronic States from Theoretical Calculations)

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