Physics behind the Barrier to Internal Rotation of an Acetyl Chloride Molecule: A Combined Approach from Density Functional Theory, Car–Parrinello Molecular Dynamics, and Time-Resolved Wavelet Transform Theory

Abstract

The physics behind the barriers to internal rotation of acetyl chloride (AC) molecule has been reported. The AC molecule closely resembles the molecular structure of acetaldehyde; the only subtle difference is the presence of a heavy chlorine atom in place of the hydrogen atom of the aldehyde group for the latter. This paper aims to study the effect of substitution of the heavy chlorine atom on the barrier energetics of the AC molecule. The reason behind the barrier for the AC molecule has been estimated for the first time from the unified approach using barrier energetics, natural bond orbital, nuclear virial, and relaxation analyses using density functional theory, Car–Parrinello molecular dynamics, and wavelet transform theory. Complete analyses reveal the concomitant relaxations of both the in-plane C methyl –C 1 and C methyl –H 4 bonds toward understanding the origin of the barrier due to internal rotation for the AC molecule. The large negative value of “ V 6 ” further suggests that both the abovementioned degrees of freedom are coupled with the −CH 3 torsional vibration of the molecule. The coupling matrix ( H 12 ) element has also been estimated. Time-resolved band stretching frequencies of C methyl –C 1 and C 1 –Cl 3 bonds of the AC molecule, as obtained from wavelet transformation analysis, primarily preclude the possibility of coupling between the C 1 –Cl 3 bond and the torsional motion associated with the methyl group of the molecule.

Adsorption of 4-Mercapto Pyridine with Gold Nanoparticles Embedded in the Langmuir–Blodgett Film Matrix of Stearic Acid: SERS, XPS Studies Aided by Born–Oppenheimer on the Fly Dynamics, Time–Resolved Wavelet Transform Theory, and DFT

“…The mother wavelet ψ( t ) is represented as 42 Here, the parameters ω 0 and σ are considered from previous literature. 36 , 43 Successful applications of the above functional form of the mother wavelet ψ( t ) as reported elsewhere and are known to reproduce the Fourier power spectrum accurately. 36 , 42 − 44 …”

“… 36 , 43 Successful applications of the above functional form of the mother wavelet ψ( t ) as reported elsewhere and are known to reproduce the Fourier power spectrum accurately. 36 , 42 − 44 …”

“…The intensities of the Raman bands ( I Raman ) have been estimated from the differential Raman scattering cross section (DRSC) ( dσ / dΩ ) values using the following expression: 34 − 36 where σ and Ω signify the scattering cross section and the solid angle at which the scattered light signal is collected, while h , c , k B , and T represent the Planck constant, speed of light, Boltzmann constant, and Kelvin temperature, respectively. The frequencies (in cm –1 ) of the incident light and the “ i th” vibrational mode are depicted by ω 0 and ω i , respectively.…”

“…The vibrational signatures of 4MPyH and 4MPyD in the vicinity of the Au cluster were obtained from the Fourier transform of the trajectories so generated from the BO-OF-MD calculations. 36 The stretching distances of atoms as a function of time linked with the vibrational modes of the molecule were elicited from the BO-OF-MD trajectories. The VDOS of the corresponding normal modes were then attained with the aid of Fourier transformation.…”

“…The wavelet transform W n ( s ) in the reciprocal space is expressed as 36 where ω k represents the angular frequency for the k th normal mode and F k and ψ̂ are the Fourier transformations of the time series F n and the mother wavelet ψ( t ), respectively. The mother wavelet ψ( t ) is represented as 42 Here, the parameters ω 0 and σ are considered from previous literature.…”