Resolving the anomalous infrared spectrum of the MeCN-HCl molecular cluster using ab Initio molecular dynamics

TY - JOUR

T1 - Resolving the anomalous infrared spectrum of the MeCN-HCl molecular cluster using ab Initio molecular dynamics

AU - Bork, Nicolai Christian

AU - Loukonen, Ville

AU - Kjærgaard, Henrik Grum

AU - Vehkamäki, Hanna

N1 - Correction: http://dx.doi.org/10.1039/C5CP90150B

PY - 2014/10/22

Y1 - 2014/10/22

N2 - We present a molecular dynamics (MD) based study of the acetonitrile-hydrogen chloride molecular cluster in the gas phase, aimed at resolving the anomalous features often seen in infrared spectra of hydrogen bonded complexes. We find that the infrared spectrum obtained from the Fourier transform of the electric dipole moment autocorrelation function converges very slowly due to the floppy nature of the complex. Even after 55 picoseconds of simulation, significant differences in the modelled and experimental spectrum are seen, likely due to insufficient configurational sampling. Instead, we utilize the MD trajectory for a structural based analysis. We find that the most populated values of the N-H-Cl angle are around 162°. The global minimum energy conformation at 180.0° is essentially unpopulated. We re-model the spectrum by combining population data from the MD simulations with optimizations constraining the N-H-Cl angle. This re-modelled spectrum is in excellent accordance with the experimental spectrum and we conclude that the observed spectral anomaly is due to the dynamics of the N-H-Cl angle.

AB - We present a molecular dynamics (MD) based study of the acetonitrile-hydrogen chloride molecular cluster in the gas phase, aimed at resolving the anomalous features often seen in infrared spectra of hydrogen bonded complexes. We find that the infrared spectrum obtained from the Fourier transform of the electric dipole moment autocorrelation function converges very slowly due to the floppy nature of the complex. Even after 55 picoseconds of simulation, significant differences in the modelled and experimental spectrum are seen, likely due to insufficient configurational sampling. Instead, we utilize the MD trajectory for a structural based analysis. We find that the most populated values of the N-H-Cl angle are around 162°. The global minimum energy conformation at 180.0° is essentially unpopulated. We re-model the spectrum by combining population data from the MD simulations with optimizations constraining the N-H-Cl angle. This re-modelled spectrum is in excellent accordance with the experimental spectrum and we conclude that the observed spectral anomaly is due to the dynamics of the N-H-Cl angle.

U2 - 10.1039/c4cp03828b

DO - 10.1039/c4cp03828b

M3 - Journal article

C2 - 25312587

SN - 1463-9076

VL - 16

SP - 24685

EP - 24690

JO - Physical Chemistry Chemical Physics

JF - Physical Chemistry Chemical Physics

IS - 45

ER -