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From Spectroscopic Insights to Structural Wonders: A Theme Issue Dedicated to Professor Jaan Laane

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Molecular Structure".

Deadline for manuscript submissions: closed (28 February 2025) | Viewed by 6704

Special Issue Editors


E-Mail Website1 Website2
Guest Editor
1. Department of Chemistry, Coimbra Chemistry Center, University of Coimbra, Coimbra, Portugal
2. Faculty of Sciences & Letters, Department of Physics, Istanbul Kultur University, Istanbul, Turkey
Interests: photochemistry; molecular cryo- and biospectroscopy; quantum chemistry; molecular structure; photophysics; chemometrics
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Special Issue Information

Dear Colleagues,

This Special Issue of Molecules is dedicated to Professor Jaan Laane for his contributions to the field of Spectroscopy.

Jaan Laane was born in Estonia on 20 June 1942. When he was two years old, he and his family fled from the Soviets, winding up in a displaced persons camp near Augsburg, Germany. In 1949, the family immigrated to the USA, settling soon in the small town of Polo, Illinois.  After graduating from high school, where he was class valedictorian, Laane attended the University of Illinois (Urbana) as an Alfred P. Sloan National Scholar and as a James Scholar. He graduated with Highest Distinction in Chemistry in 1964 and received the Kendall Award as the top senior chemistry major. As an undergraduate, he worked for three years under Professor Theodore L. Brown carrying out experiments in infrared spectroscopy and organotin synthesis. Following his first of three summers working at Los Alamos Scientific Laboratory (with Llewelyn Jones), he began graduate work at MIT as a National Science Foundation and Woodrow Wilson Fellow. Working in the laboratory of Professor Richard C. Lord, and also under the guidance of Professor Dietman Seyferth for organosilicon synthesis, Laane synthesized silacyclobutane and several other new compounds and studied their vibrational spectra. He wrote an original computer program to accurately calculate the quantum energy levels for ring-puckering vibrations with quartic/quadradic potential functions. He received his Ph.D. in 1967, along with the Kodak Award as the top graduate student in the chemistry department at MIT.

Following a year at Tufts University, Laane moved to Texas A&M University where he soon was promoted to Associate Professor (1972) and Full Professor (1976) of Chemistry. He is now Professor Emeritus of Chemistry and of Physics and Astronomy. His research there has focused on vibrational spectroscopy and the determination of vibrational potential energy surfaces in both ground and excited electronic states. He has been at the forefront of advancing both the fundamental theoretical understanding of molecular vibrations and structures, as well as the experimental methodology in these areas. He has made significant contributions to the understanding of singlet and triplet electronic excited states, to bonding of nitrogen–oxygen compounds, and to Raman difference spectroscopy. He has more than 340 publications, including four books and over a dozen book chapters.  He is editor of the 2009 book “Frontiers of Molecular Spectroscopy,” a 700 pages text with 19 chapters by leading scientists published by Elsevier. He followed this up with an updated book in 2019: “Frontiers and Advances of Molecular Spectroscopy”. He has also made more than 600 presentations, including plenary and invited lectures at chemistry and spectroscopy conferences in the United States and at dozens of other countries. In 2005, he received the prestigious E. R. Lippincott Award sponsored jointly by the Optical Society (OSA), Society for Applied Spectroscopy (SAS), and the Coblentz Society.  This was presented for “significant contributions to vibrational spectroscopy as judged by his influence on other scientists.” He was cited for “innovative use of vibrational spectroscopy to determine molecular structures and to unravel complex intramolecular dynamics.” In 2017, he received the top award from the Society for Applied Spectroscopy, the Honorary Member Award, for lifetime contributions to the field of spectroscopy. In 1999–2000 he held the Welch Foundation Lectureship, and he has held other lectureships in Japan, Germany, Spain, South Korea, Taiwan, Finland, Belgium, and Estonia as well as the USA. His research laboratory has synthesized a large number of new organosilicon and other cyclic compounds and fully analyzed their vibrational spectra, including the determination of their potential energy surfaces for conformationally important vibrations. He has been at the forefront of writing computer programs for calculating both the kinetic energy and potential energy functions for one-, two-, and three-dimensional problems. “Laane’s Tables,” published in 1970, and his programs for calculating periodic potential functions for internal rotations and pseudorotations have been widely distributed to and utilized by many dozens of laboratories around the world. These works have been cited more than 500 times. Laane has supervised the research of more than 40 Ph.D. students and more than 60 undergraduates. Numerous post-docs and visiting professors from around the world have also worked in his laboratories. Professor Laane is a Fellow of the American Physical Society, Society for Applied Spectroscopy, and the American Institute of Chemists. He received the Alexander von Humboldt U.S. Senior Scientist Award in 1979 at the very young age of 37, and he received a Texas A&M teaching award in 1982.  He is an elected member of the Estonian Academy of Sciences and received one of the first honorary D.Sc. degrees from the University of Tartu in 2000. At Texas A&M, he was Chair of the Physical and Nuclear Chemistry Division for many years, and he served as Associate Dean of Science and Speaker of the Faculty Senate.  He also played the leading role in establishing a Texas A&M campus in Japan while he was Director of the Institute for Pacific Asia in the 1980s. In 1994, he organized and chaired the NATO workshop on “Structures and Conformations of Non-Rigid molecules” in Ulm, Germany. In 2007–2009 he served as President of the Alexander von Humboldt Association of America (AvHAA) and in 2008 he organized and chaired the Humboldt Symposium for eminent scientists on “The Universe and the World Arounds Us.” Laane served as Editor for the Journal of Molecular Structure from 1994 to 2019 and served on the EUCMOS International Advisory Board during this same period. He has also served on the editorial boards of several other journals and on the organizing committees of international conferences.

Knowing Professor Jaan Laane for several years, we are very pleased to give all his colleagues and friends the opportunity to celebrate his scientific career by contributing to this Special Issue dedicated to honoring his achievements in these fields of research.

Prof. Dr. Rui Fausto
Prof. Dr. Gulce Ogruc Ildiz
Guest Editors

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Keywords

  • infrared and Raman spectroscopy
  • quantum chemical calculations
  • molecular structure
  • rotational spectroscopy
  • photochemistry
  • applied spectroscopy

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Published Papers (11 papers)

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Research

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15 pages, 3465 KiB  
Article
A Pure Rotational Spectroscopic Study of Two Nearly-Equivalent Structures of Hexafluoroacetone Imine, (CF3)C=NH
by Daniel A. Obenchain, Beppo Hartwig, Daniel J. Frohman, G. S. Grubbs II, B. E. Long, Wallace C. Pringle, Stewart E. Novick and S. A. Cooke
Molecules 2025, 30(9), 2051; https://doi.org/10.3390/molecules30092051 - 5 May 2025
Viewed by 130
Abstract
Rotational spectra for hexafluoroacetone imine, the singly substituted 13C isotopologues, and the 15N isotopologue, have been recorded using both cavity and chirped pulse Fourier transform microwave spectrometers. The spectra observed present as being doubled with separations between each pair of transitions [...] Read more.
Rotational spectra for hexafluoroacetone imine, the singly substituted 13C isotopologues, and the 15N isotopologue, have been recorded using both cavity and chirped pulse Fourier transform microwave spectrometers. The spectra observed present as being doubled with separations between each pair of transitions being on the order of a few tens of kilohertz which is consistent with a large amplitude motion producing two torsional substates. The observed splitting is most likely due to the combined motions of the CF3 groups, for which the calculated barrier is small. However, no transitions between states could be observed and, similarly, no Coriolis coupling parameters were required to achieve a satisfactory fit for the transition frequencies. Hence, and somewhat curiously, the two states have been fit independently of each other such that the two states may simply be considered near-equivalent conformers. The structural properties of hexafluoroacetone imine are compared with two isoelectronic molecules hexafluoroisobutene and hexafluoroacetone. Rotational constants, quartic centrifugal distortion constants, and the 14N nuclear electric quadrupole coupling tensor have been determined and are presented together with supporting quantum chemical calculations. Full article
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16 pages, 3975 KiB  
Article
Perfluoropropionic Acid (CF3CF2C(O)OH): Three Conformations and Dimer Formation
by Carlos O. Della Védova, Rosana M. Romano, Hans-Georg Stammler and Norbert W. Mitzel
Molecules 2025, 30(9), 1887; https://doi.org/10.3390/molecules30091887 - 23 Apr 2025
Viewed by 181
Abstract
Perfluoropropionic acid (CF3CF2C(O)OH) has been investigated with a focus on its complex structural properties. As a formal derivative of propanoic acid, the incorporation of fluorine atoms imparts unique structural features, including three distinct monomeric conformations and a dimeric structure. [...] Read more.
Perfluoropropionic acid (CF3CF2C(O)OH) has been investigated with a focus on its complex structural properties. As a formal derivative of propanoic acid, the incorporation of fluorine atoms imparts unique structural features, including three distinct monomeric conformations and a dimeric structure. This study presents experimental findings, supported by computational modeling, to explore these characteristics. The analysis includes an FTIR study of the isolated species in an Ar-cryogenic matrix and the low-temperature determination of its crystalline structure using single-crystal X-ray diffraction. Full article
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23 pages, 3919 KiB  
Article
Vibrational Properties of Doped P3HT Chains in Solution: Insight into the Doping Mechanism from Infrared IRAV and Raman RaAV Bands
by Kaiyue Hu, Sara Doti, Luigi Brambilla, Mirella Del Zoppo, Chiara Castiglioni and Giuseppe Zerbi
Molecules 2025, 30(7), 1403; https://doi.org/10.3390/molecules30071403 - 21 Mar 2025
Viewed by 205
Abstract
Chemical doping is a well-established technique for increasing the electrical conductivity of polyconjugated polymers, and its effectiveness can be assessed through IR spectroscopy, thanks to the rise of the so-called IRAVs (infrared activated vibrations), which prove the formation of polarons on the polymer [...] Read more.
Chemical doping is a well-established technique for increasing the electrical conductivity of polyconjugated polymers, and its effectiveness can be assessed through IR spectroscopy, thanks to the rise of the so-called IRAVs (infrared activated vibrations), which prove the formation of polarons on the polymer chain. While the mechanism of the IRAVs activation has been widely explored in the past, several peculiar features remain unclear. Changes in the Raman spectrum of doped polymers (RaAV, Raman activated vibrations) are widely used as well for monitoring the doping process, but the interpretation is often limited to purely empirical correlations. By means of an experimental campaign on doped regio-regular poly(3-hexylthiophene-2,5-diyl) (P3HT) samples in chloroform solution and on the solid samples cast from the same solutions, this paper presents for the first time a thorough comparative analysis of IRAVs and RaAVs, aiming at a unified description of the structure of doped P3HT. In particular, we will discuss the effect of the doping level on the vibrational features of the polymer and the dopant so that spectroscopic markers can be found to be used in the identification of the presence of ICT (integer charge transfer) complexes in different doping regimes. This study demonstrates that combining IR, Raman, and UV-Vis-NIR spectroscopies provides a powerful, complementary set of tools to diagnose not only the doping level but also the detailed molecular and supramolecular structure of the doped P3HT, useful for the development of structure/properties relationships in the perspective of the optimization of the charge transport performances. Full article
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12 pages, 2762 KiB  
Article
Ultrasensitive Chemical Analysis on Gold Nano Popcorn Substrate Using Digital Surface-Enhanced Raman Scattering
by Soyeon Lee and Jaebum Choo
Molecules 2025, 30(6), 1371; https://doi.org/10.3390/molecules30061371 - 19 Mar 2025
Viewed by 321
Abstract
This study presents a digital surface-enhanced Raman scattering (SERS) method to enhance the sensitivity of SERS detection for low-concentration analytes. Conventional SERS analysis using average Raman intensity faces limitations in distinguishing low concentrations due to the substrate’s sparse distribution of target molecules. To [...] Read more.
This study presents a digital surface-enhanced Raman scattering (SERS) method to enhance the sensitivity of SERS detection for low-concentration analytes. Conventional SERS analysis using average Raman intensity faces limitations in distinguishing low concentrations due to the substrate’s sparse distribution of target molecules. To overcome this challenge, we used a binary code-based data analysis approach. Gold nano popcorn substrates were utilized for high-sensitivity detection, with malachite green isothiocyanate (MGITC) as the target molecule. Raman mapping data were analyzed using both the conventional average Raman intensity method and the proposed digital SERS approach. In the digital SERS method, a threshold value was established based on the mean and standard deviation of Raman signals in the absence of target molecules. Pixels with Raman intensities exceeding this threshold were assigned a value of “1”, while those below were assigned “0”. Quantification was then performed based on these digital counts corresponding to MGITC concentrations. Our results demonstrate that the digital SERS method significantly improved the ability to distinguish and quantify analytes in low-concentration ranges that were indiscernible using the conventional approach. This analytical technique shows promise for ultrasensitive chemical analysis and expands the capabilities of SERS-based detection methods, potentially revolutionizing the field of trace analyte detection. Full article
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15 pages, 4406 KiB  
Article
Two Coupled Low-Barrier Large Amplitude Motions in 3,5-Dimethylanisole Studied by Microwave Spectroscopy
by Safa Khemissi, Lynn Ferres and Ha Vinh Lam Nguyen
Molecules 2025, 30(6), 1195; https://doi.org/10.3390/molecules30061195 - 7 Mar 2025
Viewed by 389
Abstract
The microwave spectrum of 3,5-dimethylanisole was recorded using a pulsed molecular jet Fourier transform microwave spectrometer, covering the frequency range from 2.0 to 26.5 GHz. Splittings from internal rotations of the syn-m and anti-m-methyl groups were observed, analyzed, [...] Read more.
The microwave spectrum of 3,5-dimethylanisole was recorded using a pulsed molecular jet Fourier transform microwave spectrometer, covering the frequency range from 2.0 to 26.5 GHz. Splittings from internal rotations of the syn-m and anti-m-methyl groups were observed, analyzed, and modeled using the XIAM and the ntop programs for a data set including 622 rotational lines. The torsional barriers of the syn-m and anti-m-methyl groups were determined to be 58.62367(53) cm−1 and 36.28449(69) cm−1, respectively. The low barriers to internal rotation of both methyl groups posed significant challenges for spectral analysis and modeling. The successful assignment was achieved using combination difference loops and separately fitting the five torsional components. Comparing the torsional barriers observed in various toluene derivatives with methyl groups at meta-positions supports the assumption that electrostatic effects contribute more significantly than steric effects in the low-barrier cases of aromatic molecules. Full article
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12 pages, 2467 KiB  
Article
Non-Isothermal Melt Crystallization of a Biodegradable Polymer Studied by Two-Dimensional Infrared Correlation Spectroscopy
by Isao Noda
Molecules 2025, 30(5), 1131; https://doi.org/10.3390/molecules30051131 - 1 Mar 2025
Viewed by 492
Abstract
The non-isothermal melt crystallization process of poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoateate] (PHBHx) was monitored using attenuated total reflection infrared (ATR IR) measurement. The resulting time- and temperature-dependent spectra were subjected to the two-dimensional correlation spectroscopy (2D-COS) analysis. The C=O stretching region of the PHBHx sample [...] Read more.
The non-isothermal melt crystallization process of poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoateate] (PHBHx) was monitored using attenuated total reflection infrared (ATR IR) measurement. The resulting time- and temperature-dependent spectra were subjected to the two-dimensional correlation spectroscopy (2D-COS) analysis. The C=O stretching region of the PHBHx sample consisted of several distinct IR contributions attributable to the population of amorphous component, well-ordered type I lamellar crystal, and less ordered inter-lamellar type II crystal. The spectral intensity change in type I crystal occurs in the earlier stage of the crystallization at a higher temperature range compared to the overall intensity decrease in the amorphous component occurring throughout the crystallization process. The growth of the type II crystal started in a later stage at a lower temperature than the creation of the type I crystal. An early decrease in a small but distinct portion of the amorphous component may be related to a crystallization precursor species with some level of molecular order. Hetero-mode correlation analyses revealed that the crystalline band intensity changes in the C-H stretching and fingerprint regions all occur later than the population changes in crystalline species reflected by the carbonyl stretching bands. This observation suggests that the spectral intensity changes in the C-H stretching and fingerprint regions do not directly represent the population dynamics of the crystalline and amorphous species but probe instead the molecular state of the crystalline entities still undergoing the evolutionary changes. Full article
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26 pages, 6238 KiB  
Article
Reversal in Solvatochromism, enol-imine/keto-amine Tautomerism and (E)-(Z) Photoisomerizations in a Benzylidene Aniline Schiff Base Derivative in Different Solvents
by İsa Sıdır, Yadigar Gülseven Sıdır, Halil Berber, Maria L. Ramos, Licínia L. G. Justino and Rui Fausto
Molecules 2025, 30(3), 745; https://doi.org/10.3390/molecules30030745 - 6 Feb 2025
Viewed by 732
Abstract
A novel Schiff base, (E)-4-acetyl-N-(4-hydroxy-3-methoxybenzylidene)aniline (abbreviated as ANHMA), was synthesized and characterized using infrared and 1H- and 13C-NMR spectroscopies. Optical properties in different solvents were evaluated using UV-vis absorption spectroscopy. The compound is shown to [...] Read more.
A novel Schiff base, (E)-4-acetyl-N-(4-hydroxy-3-methoxybenzylidene)aniline (abbreviated as ANHMA), was synthesized and characterized using infrared and 1H- and 13C-NMR spectroscopies. Optical properties in different solvents were evaluated using UV-vis absorption spectroscopy. The compound is shown to exhibit both positive and negative solvatochromism with reversal occurring for solvents with ET(30)~45 (e.g., DMSO). The solvatochromic behavior of the compound was found to be strongly dependent on the hydrogen bond abilities and polarizability of the solvent, the observed reversal in solvatochromism being explained by the change in the dominant solvent effects in non-polar and polar–aprotic solvents (H-bond acceptor ability of the solvent and polarizability) compared to polar–protic solvents (H-bond donor ability), according to the developed Catalán multiparametric solvatochromic model. In all freshly prepared solutions studied, the (E)-enol-imine tautomer of the compound was found to strongly predominate over the keto-amine tautomeric forms, the latter increasing their populations over time in the presence of H-bond donor/acceptor species. Irradiation of ANHMA with UV light (λ ≥ 311 nm) was also investigated in several solvents and shown to follow a general pattern, with the conversion of the (E)-enol-imine tautomer into the keto-amine forms in a solvent-mediated enol-imine/keto-amine tautomerism, and (Z)→(E) C=C isomerization between the keto-imine forms. The experimental results received support from an extensive series of calculations on the structure and UV-vis spectra of the relevant tautomeric/isomeric forms of the compound performed at the DFT(B3LYP)/6-311++G(d,p) level of approximation (including time-dependent DFT calculations and solvent consideration). Full article
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9 pages, 527 KiB  
Article
Scaling of Rotational Constants
by Denis S. Tikhonov, Colin J. Sueyoshi, Wenhao Sun, Fan Xie, Maria Khon, Eva Gougoula, Jiayi Li, Freya Berggötz, Himanshi Singh, Christina M. Tonauer and Melanie Schnell
Molecules 2024, 29(24), 5874; https://doi.org/10.3390/molecules29245874 - 12 Dec 2024
Cited by 1 | Viewed by 722
Abstract
This manuscript introduces the concept of scaling factors for rotational constants. These factors are designed to bring computed equilibrium rotational constants closer to experimentally fitted ground-state-averaged rotational constants. The parameterization of the scaling factors was performed for several levels of theory, namely DF-D [...] Read more.
This manuscript introduces the concept of scaling factors for rotational constants. These factors are designed to bring computed equilibrium rotational constants closer to experimentally fitted ground-state-averaged rotational constants. The parameterization of the scaling factors was performed for several levels of theory, namely DF-Dn/def2-mVP (DF=B3LYP,PBE0, n=3(BJ),4, m=S,TZ), PBEh-3c, and r2SCAN-3c. The obtained scaling factors systematically improved the consistency between the theoretical and experimental rotational constants. Full article
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15 pages, 3731 KiB  
Article
Infrared Matrix-Isolation and Theoretical Studies of the Reactions of Bis(benzene)chromium with Ozone
by Roger W. Kugel and Bruce S. Ault
Molecules 2024, 29(15), 3583; https://doi.org/10.3390/molecules29153583 - 29 Jul 2024
Viewed by 1203
Abstract
Reactions of bis(benzene)chromium (Bz2Cr) and ozone (O3) were studied using low-temperature argon matrix-isolation infrared spectroscopy with supporting DFT calculations. When Bz2Cr and O3 were co-deposited, they reacted upon matrix deposition to produce two new prominent peaks [...] Read more.
Reactions of bis(benzene)chromium (Bz2Cr) and ozone (O3) were studied using low-temperature argon matrix-isolation infrared spectroscopy with supporting DFT calculations. When Bz2Cr and O3 were co-deposited, they reacted upon matrix deposition to produce two new prominent peaks in the infrared spectrum at 431 cm1 and 792 cm1. These peaks increased upon annealing the matrix to 35 K and decreased upon UV irradiation at λ = 254 nm. The oxygen-18 and mixed oxygen-16,18 isotopic shift pattern of the peak at 792 cm1 is consistent with the antisymmetric stretch of a symmetric ozonide species. DFT calculations of many possible ozonide products of this reaction were made. The formation of a hydrogen ozonide (H2O3) best fits the original peaks and the oxygen-18 isotope shift pattern. Energy considerations lead to the conclusion that the chromium-containing product of this reaction is the coupled product benzene-chromium-biphenyl-chromium-benzene (BzCrBPCrBz). 2Bz2Cr+O3H2O3+BzCrBPCrBz, Ecalc=52.13kcal/mol. Full article
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13 pages, 522 KiB  
Article
Equilibrium Values for the Si-H Bond Length and Equilibrium Structures of Silyl Iodide and Halosilylenes
by Jean Demaison and Jacques Liévin
Molecules 2024, 29(13), 3101; https://doi.org/10.3390/molecules29133101 - 28 Jun 2024
Cited by 1 | Viewed by 1065
Abstract
The equilibrium structures of silyl iodide, SiH3I, and silylene halides, SiHX (X = F, Cl, Br, I), were determined by using the mixed regression method, where approximate values of the rotational constants are supplemented by the structural parameters of a different [...] Read more.
The equilibrium structures of silyl iodide, SiH3I, and silylene halides, SiHX (X = F, Cl, Br, I), were determined by using the mixed regression method, where approximate values of the rotational constants are supplemented by the structural parameters of a different origin. For this goal, it is shown that the r(Si-H) bond length can be determined by using the isolated SiH stretching frequency and that an accurate estimation of the bond angles is obtained by an MP2 calculation with a basis set of triple zeta quality. To check the accuracy of the experimental structures, they were also optimized by means of all electron CCSD(T) calculations using basis sets of quadruple zeta quality. Full article
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Review

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23 pages, 16843 KiB  
Review
Beyond the Harmonic Oscillator; Highlights of Selected Studies of Vibrational Potential Energy Functions
by Esther J. Ocola and Jaan Laane
Molecules 2025, 30(7), 1492; https://doi.org/10.3390/molecules30071492 - 27 Mar 2025
Viewed by 247
Abstract
Although the harmonic oscillator model has found wide use in physics and chemistry, there are more interesting potential energy functions (PEFs) which can tell us a great deal about molecular structure and energetics. In the present work, we show that for selected systems [...] Read more.
Although the harmonic oscillator model has found wide use in physics and chemistry, there are more interesting potential energy functions (PEFs) which can tell us a great deal about molecular structure and energetics. In the present work, we show that for selected systems simple one- and two-dimensional potential functions can be used to very accurately fit detailed spectroscopic data and provide extensive additional information. Results for molecular inversion, ring puckering, the anomeric effect, pseudorotation, triplet-state puckering, internal rotation, and π-type hydrogen bonding in ground and excited electronic states are presented. Full article
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