Theoretical Study of Vibrationally Averaged Dipole Moments for the Ground and Excited C═O Stretching States of trans-Formic Acid

Abstract

Recent experimental studies of trans-formic acid (FA) in solid para-hydrogen (pH2) highlighted the importance of vibrationally averaged dipole moments for the interpretation of the high-resolution infrared (IR) spectra, in particular for the C═O stretch (ν3) mode. In this report, dipole moments for the ν3 ground (v = 0) and excited (v = 1, 2, 3, and 4) anharmonic vibrational states in trans-FA are investigated using two different approaches: a single mode approximation, where the vibrational states are obtained from the solution of the one-dimensional Schrödinger equation for the harmonic normal coordinate, and a limited vibrational configuration interaction (VCI) approximation. Density functional theory (B3LYP, BPW91) and correlated ab initio (MP2 and CCSD(T)) electronic methods were employed with a number of double- and triple-ζ and correlation consistent basis sets. Both single mode and VCI approaches show comparable agreement with experimental data, which is more dependent on the level of theory used. In particular, the BPW91/cc-pVDZ level appears to perform remarkably well. Effects of solvation of FA in solid state Ar and pH2 matrices were simulated at the BPW91/cc-pVDZ level using a conductor-like polarized continuum model (CPCM). The Ar and pH2 solid-state matrices cause quite a substantial increase in the FA dipole moments. Compared to gas-phase calculations, the CPCM model for pH2 better reproduces the experimental FA spectral shifts caused by interaction with traces of ortho-hydrogen (oH2) species in solid pH2. The validity of the single mode approach is tested against the multidimensional VCI results, suggesting that the isolated (noninteracting) mode approximation is valid up to the third vibrationally excited state (v = 3). Finally, the contribution of the ground anharmonic vibrational states of the remaining modes to the resulting ν3 single mode dipole moments is examined and discussed.

Far-Infrared Synchrotron Spectroscopy and Torsional Analysis of the Important Interstellar Molecule, Vinyl Alcohol

“…It is interesting to note that complete vibrational averaging of the dipole moment components (over the 15 vibrational modes) has a similar effect to just torsional averaging them (over ν 15 ), indicating that motion along the CC–O–H dihedral coordinate has by far the greatest effect on the dipole moment components (see Table ). Vibrational averaging of the dipole moment is also known to be important in the related molecules, HCOOH, which has been detected in the ISM, , and HOOO, which has been searched for in the ISM …”

Understanding the Phosphorylation Mechanism by Using Quantum Chemical Calculations and Molecular Dynamics Simulations

“…25–28 Solvation effects were evaluated by single-point calculations on the optimized geometries at the B3LYP 6–31G* level of theory as the geometry optimizations using the conductor-like polarized continuum model (C-PCM). 28 In the calculations, ε = 4 was used for the surrounding solvent. Frequency calculations were performed to obtain free energy corrections at 298.15 K and 1 atm pressure.…”

A DFT Study of Vibrational Spectra and Mutagenicity Predictions of Mononitrated Fluoranthenes

“…More accurate and consistent dipole moments are especially predicted with use of more diffuse functions (58). From Equation (1) is noted the inverse relationship between I IR and Q 2 .…”

“…Indeed, "the dipole moment in a particular electronic state is some function of the internuclear distance and also depends on the orientation of the molecule" (59). Paulson et al (58) showed that the average dipole moments is correlated to the vibrational states and 6.57 D). The high-intensity nitro group frequencies come as a consequence of the modulation of the dipole moment with the N O stretches reinforced by the C C and N C stretches.…”