Critical interpretation of CH- and OH- stretching regions for infrared spectra of methanol clusters (CH₃OH)n (n = 2-5) using self-consistent-charge density functional tight-binding molecular dynamics simulations

Yoshifumi Nishimura, Yuan Pern Lee, Stephan Irle, Henryk A. Witek

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Abstract

Vibrational infrared (IR) spectra of gas-phase O-H⋅⋅⋅O methanol clusters up to pentamer are simulated using self-consistent-charge density functional tight-binding method using two distinct methodologies: standard normal mode analysis and Fourier transform of the dipole time-correlation function. The twofold simulations aim at the direct critical assignment of the C-H stretching region of the recently recorded experimental spectra [H.-L. Han, C. Camacho, H. A. Witek, and Y.-P. Lee, J. Chem. Phys. 134, 144309 (2011)]. Both approaches confirm the previous assignment (ibid.) of the C-H stretching bands based on the B3LYP/ANO1 harmonic frequencies, showing that ν3, ν9, and ν2 C-H stretching modes of the proton-accepting (PA) and proton-donating (PD) methanol monomers experience only small splittings upon the cluster formation. This finding is in sharp discord with the assignment based on anharmonic B3LYP/VPT2/ANO1 vibrational frequencies (ibid.), suggesting that some procedural faults, likely related to the breakdown of the perturbational vibrational treatment, led the anharmonic calculations astray. The IR spectra based on the Fourier transform of the dipole time-correlation function include new, previously unaccounted for physical factors such as non-zero temperature of the system and large amplitude motions of the clusters. The elevation of temperature results in a considerable non-homogeneous broadening of the observed IR signals, while the presence of large-amplitude motions (methyl group rotations and PA-PD flipping), somewhat surprisingly, does not introduce any new features in the spectrum.

Original languageEnglish
Pages (from-to)94303
Number of pages1
JournalJournal of Chemical Physics
Volume141
Issue number9
DOIs
Publication statusPublished - 2014 Sep 7
Externally publishedYes

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Molecular Dynamics Simulation
Charge density
Stretching
Methanol
Molecular dynamics
Protons
infrared spectra
methyl alcohol
methylidyne
molecular dynamics
Infrared radiation
protons
Computer simulation
Fourier Analysis
Fourier transforms
simulation
dipoles
physical factors
Temperature
Vibrational spectra

ASJC Scopus subject areas

  • Medicine(all)

Cite this

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title = "Critical interpretation of CH- and OH- stretching regions for infrared spectra of methanol clusters (CH₃OH)n (n = 2-5) using self-consistent-charge density functional tight-binding molecular dynamics simulations",
abstract = "Vibrational infrared (IR) spectra of gas-phase O-H⋅⋅⋅O methanol clusters up to pentamer are simulated using self-consistent-charge density functional tight-binding method using two distinct methodologies: standard normal mode analysis and Fourier transform of the dipole time-correlation function. The twofold simulations aim at the direct critical assignment of the C-H stretching region of the recently recorded experimental spectra [H.-L. Han, C. Camacho, H. A. Witek, and Y.-P. Lee, J. Chem. Phys. 134, 144309 (2011)]. Both approaches confirm the previous assignment (ibid.) of the C-H stretching bands based on the B3LYP/ANO1 harmonic frequencies, showing that ν3, ν9, and ν2 C-H stretching modes of the proton-accepting (PA) and proton-donating (PD) methanol monomers experience only small splittings upon the cluster formation. This finding is in sharp discord with the assignment based on anharmonic B3LYP/VPT2/ANO1 vibrational frequencies (ibid.), suggesting that some procedural faults, likely related to the breakdown of the perturbational vibrational treatment, led the anharmonic calculations astray. The IR spectra based on the Fourier transform of the dipole time-correlation function include new, previously unaccounted for physical factors such as non-zero temperature of the system and large amplitude motions of the clusters. The elevation of temperature results in a considerable non-homogeneous broadening of the observed IR signals, while the presence of large-amplitude motions (methyl group rotations and PA-PD flipping), somewhat surprisingly, does not introduce any new features in the spectrum.",
author = "Yoshifumi Nishimura and Lee, {Yuan Pern} and Stephan Irle and Witek, {Henryk A.}",
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T1 - Critical interpretation of CH- and OH- stretching regions for infrared spectra of methanol clusters (CH₃OH)n (n = 2-5) using self-consistent-charge density functional tight-binding molecular dynamics simulations

AU - Nishimura, Yoshifumi

AU - Lee, Yuan Pern

AU - Irle, Stephan

AU - Witek, Henryk A.

PY - 2014/9/7

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N2 - Vibrational infrared (IR) spectra of gas-phase O-H⋅⋅⋅O methanol clusters up to pentamer are simulated using self-consistent-charge density functional tight-binding method using two distinct methodologies: standard normal mode analysis and Fourier transform of the dipole time-correlation function. The twofold simulations aim at the direct critical assignment of the C-H stretching region of the recently recorded experimental spectra [H.-L. Han, C. Camacho, H. A. Witek, and Y.-P. Lee, J. Chem. Phys. 134, 144309 (2011)]. Both approaches confirm the previous assignment (ibid.) of the C-H stretching bands based on the B3LYP/ANO1 harmonic frequencies, showing that ν3, ν9, and ν2 C-H stretching modes of the proton-accepting (PA) and proton-donating (PD) methanol monomers experience only small splittings upon the cluster formation. This finding is in sharp discord with the assignment based on anharmonic B3LYP/VPT2/ANO1 vibrational frequencies (ibid.), suggesting that some procedural faults, likely related to the breakdown of the perturbational vibrational treatment, led the anharmonic calculations astray. The IR spectra based on the Fourier transform of the dipole time-correlation function include new, previously unaccounted for physical factors such as non-zero temperature of the system and large amplitude motions of the clusters. The elevation of temperature results in a considerable non-homogeneous broadening of the observed IR signals, while the presence of large-amplitude motions (methyl group rotations and PA-PD flipping), somewhat surprisingly, does not introduce any new features in the spectrum.

AB - Vibrational infrared (IR) spectra of gas-phase O-H⋅⋅⋅O methanol clusters up to pentamer are simulated using self-consistent-charge density functional tight-binding method using two distinct methodologies: standard normal mode analysis and Fourier transform of the dipole time-correlation function. The twofold simulations aim at the direct critical assignment of the C-H stretching region of the recently recorded experimental spectra [H.-L. Han, C. Camacho, H. A. Witek, and Y.-P. Lee, J. Chem. Phys. 134, 144309 (2011)]. Both approaches confirm the previous assignment (ibid.) of the C-H stretching bands based on the B3LYP/ANO1 harmonic frequencies, showing that ν3, ν9, and ν2 C-H stretching modes of the proton-accepting (PA) and proton-donating (PD) methanol monomers experience only small splittings upon the cluster formation. This finding is in sharp discord with the assignment based on anharmonic B3LYP/VPT2/ANO1 vibrational frequencies (ibid.), suggesting that some procedural faults, likely related to the breakdown of the perturbational vibrational treatment, led the anharmonic calculations astray. The IR spectra based on the Fourier transform of the dipole time-correlation function include new, previously unaccounted for physical factors such as non-zero temperature of the system and large amplitude motions of the clusters. The elevation of temperature results in a considerable non-homogeneous broadening of the observed IR signals, while the presence of large-amplitude motions (methyl group rotations and PA-PD flipping), somewhat surprisingly, does not introduce any new features in the spectrum.

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