Comments on the concept of universal intensities in local mode theory

Burberry, M. S.; Albrecht, A. C.

doi:10.1063/1.438268

Cited by 25 publications

(24 citation statements)

References 6 publications

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“…In spite of the very bright CH fundamental σ u due to the acidic CH bond, their first overtone, to which the latter σ g + σ u mode corresponds, has an intensity insensitive to the CH bond acidity due to the so-called universal intensity concept. 69,70 This phenomenon is a consequence of the intensity cancelation of the firstand second-derivative terms of the DMF with respect to the CH bond displacement, as shown in our previous work. 71 In the NM picture, the large π g + π u combination band intensity is interpreted as a result of the intensity borrowing from the intense CH fundamental σ u due to the third-order anharmonicity (see section 4.3).…”

Section: Resultssupporting

confidence: 73%

Size-Dependent π_g + π_u Combination Band Intensities of Polyynes C_2nH₂ (n = 1–9) Analyzed by the Local CCH Bending and the Linear Response Functions

et al. 2021

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Polyynes (C 2n H 2 ) show the unusually strong π g + π u combination bands in the infrared absorption spectra. We calculated them as the first overtone of the local CCH bending; the strong intensities are interpreted as a consequence of the largeamplitude bending vibration of the acidic acetylenic hydrogen combined with the size-dependent π electron conjugation. Our theoretical calculations show that the absorption intensity increases steadily and their increase rate is gradually slowed down by increasing the number of acetylene units up to n = 9. However, the calculated vibrational wavenumber converges quickly in agreement with the experimental observation. The second-order electron density deformation caused by the local CCH bending was analyzed using the linear response functions, including the linear and nonlinear contributions, to explain the n dependence. The easily polarizable π electron density caused two kinds of deformationdominant but dark δ xx−yy type and minor but bright σ type. Both of them exhibit interesting zigzag sign alternations, consistent with the law of alternating polarity of Coulson and Longuet−Higgins. The electron density polarization in these intra-and interacetylene units induces a large axial component molecular dipole moment, contributing to the intensity that increases with n. The difference between the curvilinear and rectilinear bending coordinates is interpreted within the present theoretical scheme.

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Section: Resultssupporting

confidence: 73%

Size-Dependent π_g + π_u Combination Band Intensities of Polyynes C_2nH₂ (n = 1–9) Analyzed by the Local CCH Bending and the Linear Response Functions

et al. 2021

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“…Takahashi et al 62 calculated the integrated cross sections for the C-H stretching overtones of c-DCE and t-DCE using a local mode model in which both the potential energy surface and the dipole moment function were determined from ab initio calculations. These authors sought to explain the deviation of the t-DCE cross section from the trend observed by Burberry et al 72 of a characteristic ͑molecule-independent͒ integrated cross section per C-H bond for the second through sixth overtones. Finding the vibrational wavefunctions for two DCE isomers to be essentially identical, Takahashi et al 62 explained the experimental discrepancy through a significant difference in the calculated dipole moment functions.…”

Section: ͑3͒mentioning

confidence: 99%

Absolute surface coverage measurement using a vibrational overtone

Pipino

Hoefnagels

Watanabe

2004

The Journal of Chemical Physics

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Determination of absolute surface coverage with sub-monolayer sensitivity is demonstrated using evanescent-wave cavity ring-down spectroscopy ͑EW-CRDS͒ and conventional CRDS by employing conservation of the absolute integrated absorption intensity between gas and adsorbed phases. The first C-H stretching overtones of trichloroethylene ͑TCE͒, cis-dichloroethylene, and trans-dichloroethylene are probed using the idler of a seeded optical parametric amplifier having a 0.075 cm Ϫ1 line width. Polarized absolute adsorbate spectra are obtained by EW-CRDS using a fused-silica monolithic folded resonator having a finesse of 28 500 at 6050 cm Ϫ1 , while absolute absorption cross sections for the gas-phase species are determined by conventional CRDS. A measure of the average transition moment orientation on the surface, which is utilized for the coverage determination, is derived from the polarization anisotropy of the surface spectra. Coverage measurement by EW-CRDS is compared to a mass-spectrometer-based surface-uptake technique, which we also employ for coverage measurements of TCE on thermally grown SiO 2 surfaces. To assess the potential for environmental sensing, we also compare EW-CRDS to optical waveguide techniques developed previously for TCE detection.

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“…ℨ is equal to unity. Using eqs 4 and 5, the molecular and conformational dependence of the absorption intensities can be examined in terms of ρ (1) (r) and ρ (2) (r), including the electric anharmonicity. 32 Molecular electron density at a point r is Taylor expanded around the equilibrium OH bond distance at ΔR = 0 as follows…”

Section: R R R R ( )Dmentioning

confidence: 99%

“…If the time-dependent oscillation is considered through ΔR(t) = A sin ωt, the ρ (1) (r)ΔR and ρ (2) (r)ΔR 2 terms are responsible mostly for the fundamental and overtone absorption intensities, respectively. 46 If ρ (1) (r) and ρ (2) and lower-level overtone intensities will appear with various stereoelectronic effects.…”

Section: R R R R ( )Dmentioning

confidence: 99%

“…For overtones, there are two characteristics: the normal intensity distribution law (NIDL) 1 and the universal intensity concept (UIC). 2,3 According to the NIDL, the overtone intensities fall off exponentially with increasing vibration quantum number v, as has been discussed based on a quasiclassical method by Medvedev. 4−7 A weak substituent dependence of overtone intensities, 8,9 namely, UIC, has also been explained using a local mode model 10−12 that employs the OH displacement as the vibrational coordinate.…”

Section: Introductionmentioning

confidence: 99%

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Graphical Transition Moment Decomposition and Conceptual Density Functional Theory Approaches to Study the Fundamental and Lower-Level Overtone Absorption Intensities of Some OH Stretching Vibrations

et al. 2021

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The investigation of electron density migrations caused by molecular structure changes is of central importance in various fields of chemistry. To address this topic in general and to study absorption intensities of vibrations, we analyze sensitive dipole moment functions (DMFs) of a molecule by combining the linear response function of conceptual DFT and bond dipoles separated by the quantum theory of atoms in molecules with a graphical transition moment decomposition scheme. The fundamental intensities of OH stretching vibrations depend strongly on the substituents but only weakly on the molecular conformations. Interestingly, in some alcohols, completely opposite trends have been observed for the lower-level overtone intensities: a weak substituent dependence but a stronger conformation dependence. It is well known that the formation of a hydrogen-bonded complex increases the OH stretching fundamental intensity, but less well known is the decrease in their overtone intensities. To investigate these characteristics comprehensively, we calculated their intensities (Δv = 1, 2, and 3) for conformers of ethanol and trifluoroethanol (TFE) and hydrogen-bonded phenol (PhOH) systems via the DFT method in the local mode model for the OH stretching coordinate ΔR. Their first and second derivatives of the electron density with respect to ΔR were calculated and interpreted using their bond moments. For ethanol and TFE, the OH, CC, and CH bond moments were found to make an important contribution to the molecular DMF derivatives parallel to the OH bond. The OH bond contributes only to the first derivative of DMF, and its conformational dependence is determined by the magnitude of the charge polarization of each structure. The electron density derivatives in the CC bond region were largely maintained during the internal rotation; thus, their conformation-dependent contributions were expressed by a geometrical factor of the CC bond direction. The CH bond at the antiperiplanar position of the OH bond was found to make a remarkably large contribution to the second derivative of DMF in the gauche conformer. The importance of electron density migration on substituents was also identified in the hydrogen-bonded phenol, in which the π-electron density change on the aromatic ring was clearly shown. This migration creates the DMF derivatives both perpendicular and parallel to the OH bond and strongly affects the absorption intensities. In all the cases, some bond moments on the substituents contribute to the first and second DMF derivatives in a structure-dependent manner, thus explaining their stereoelectronic effects.

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Comments on the concept of universal intensities in local mode theory

Abstract: Tetramethylsilane (TMS) Spectra were obtained with a Cary 14-spectropholometer. The intensities in the primary C-H LM overtones and the neighboring sidebands of TMS are given and discussed in terms of the Universal cconcept of intensities. (AIP)

Cited by 25 publications

References 6 publications

Size-Dependent π_g + π_u Combination Band Intensities of Polyynes C_2nH₂ (n = 1–9) Analyzed by the Local CCH Bending and the Linear Response Functions

Size-Dependent π_g + π_u Combination Band Intensities of Polyynes C_2nH₂ (n = 1–9) Analyzed by the Local CCH Bending and the Linear Response Functions

Absolute surface coverage measurement using a vibrational overtone

Graphical Transition Moment Decomposition and Conceptual Density Functional Theory Approaches to Study the Fundamental and Lower-Level Overtone Absorption Intensities of Some OH Stretching Vibrations

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Comments on the concept of universal intensities in local mode theory

Abstract: Tetramethylsilane (TMS) Spectra were obtained with a Cary 14-spectropholometer. The intensities in the primary C-H LM overtones and the neighboring sidebands of TMS are given and discussed in terms of the Universal cconcept of intensities. (AIP)

Cited by 25 publications

References 6 publications

Size-Dependent πg + πu Combination Band Intensities of Polyynes C2nH2 (n = 1–9) Analyzed by the Local CCH Bending and the Linear Response Functions

Size-Dependent πg + πu Combination Band Intensities of Polyynes C2nH2 (n = 1–9) Analyzed by the Local CCH Bending and the Linear Response Functions

Absolute surface coverage measurement using a vibrational overtone

Graphical Transition Moment Decomposition and Conceptual Density Functional Theory Approaches to Study the Fundamental and Lower-Level Overtone Absorption Intensities of Some OH Stretching Vibrations

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Product

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Size-Dependent π_g + π_u Combination Band Intensities of Polyynes C_2nH₂ (n = 1–9) Analyzed by the Local CCH Bending and the Linear Response Functions

Size-Dependent π_g + π_u Combination Band Intensities of Polyynes C_2nH₂ (n = 1–9) Analyzed by the Local CCH Bending and the Linear Response Functions