Finite-Temperature Effects on the Stability and Infrared Spectra of HCl(H₂O)₆ Clusters

Abstract

Theoretical studies of the interaction of HCl with small water clusters have so far neglected the effect of temperature, which ranges from a few tens of kelvin in cluster experiments, up to about 250 K in typical atmospheric conditions. We study the dynamical behavior of a selected set of HCl(H 2 O) 6 clusters, representative of undissociated and dissociated configurations, by means of DFT-based first principles molecular dynamics. We find that the thermodynamcal stability of different configurations can be affected by temperature. We also present the infrared spectra of dissociated and undissociated configurations at 200 K and discuss the origin of the spectral features.

Further considerations of cosmic ray modulation of infra-red radiation in the atmosphere

“…These reveal that, as well as the shorter O-H wavelength bond stretching effect, at the long wavelength end of this spectrum there is IR absorption caused by intermolecular vibrations. The Goss et al experiment did not show any increased amplitude in the main 9mm absorption band of the AL experiment, but these and other results support absorption of water clusters in our experiment's sidebands 30,31 This offers a potential explanation of the longer-than-expected decay time constant, and even of the continued rise in absorption as large n clusters split into multiple clusters of smaller n. There is also some evidence that some of the better-studied smaller oligomers, such as the tetramer, do have absorption lines in the main band of the AL experiment 32 . The time constants for these neutral cluster changes are predicted to be of order several hundreds of seconds 28 and hence this does provide a real possibility of explaining the delay before peak DLW absorption.…”

Infrared Spectra of HCl(H2O)n Clusters from Semiempirical Born–Oppenheimer Molecular Dynamics Simulations

“…19 Finite-temperature effects on the stability and IR spectra of undissociated and dissociated HCl(H 2 O) 6 clusters were also studied using "first-principles" MD simulations. 20 Recently, new experimental measurements have provided direct evidence for the presence of dissociated HCl molecules in HCl(H 2 O) n clusters with n ≥ 4. 8,21 In a previous study, we investigated the low-energy structures of HCl(H 2 O) 4−10 clusters.…”

Temperature dependence of vibrational modes of CH3CC(ads) and I(ads) coadsorbed on Ag(111): Ab initio molecular dynamics approach

“…[9] Consequently, it was verified that this stable structural model of CH 3 AC (b) BC (a)(ads) and I (ads) coadsorbed onto the Ag(111) surface, in which the ACAC (b) BC (a) axis is completely upright based on a reasonable correlation between the experimental RAIRS and the calculated IR frequencies, with a scaling factor of 0.9612 to correct the systematic error in their finite cluster static calculations with harmonic approximation. To improve this structural model, both the single-layer Ag 19 hexagonal cluster and the doublelayer Ag 22 (14,8) cluster, [10] for which 14 and 8 represent the numbers of the surface and subsurface layer atoms, respectively, were further used to simulate CH 3 AC (b) BC (a)(ads) adsorbed on the Ag(111) surface at the same level of DFT calculation. This more realistic calculation of the Ag 22 (14,8) cluster indicates that the triple bridge of CH 3 AC (b) BC (a) AAg(111) is noticeably asymmetric and that the ACAC (b) BC (a) A axis is not entirely upright, having a titled angle of $ 16 relative to the surface normal.…”

“…To improve this structural model, both the single-layer Ag 19 hexagonal cluster and the doublelayer Ag 22 (14,8) cluster, [10] for which 14 and 8 represent the numbers of the surface and subsurface layer atoms, respectively, were further used to simulate CH 3 AC (b) BC (a)(ads) adsorbed on the Ag(111) surface at the same level of DFT calculation. This more realistic calculation of the Ag 22 (14,8) cluster indicates that the triple bridge of CH 3 AC (b) BC (a) AAg(111) is noticeably asymmetric and that the ACAC (b) BC (a) A axis is not entirely upright, having a titled angle of $ 16 relative to the surface normal. [10] Finally, the small deviation from linearity of…”

“…Therefore, in this study, the IR active vibrational modes of CH 3 AC (b) BC (a)(ads) and I (ads) coadsorbed on the Ag(111) surface will be reinvestigated by performing ab initio molecular dynamics (AIMD) simulations in connection with the Fourier transform of the dipole moment (aligned perpendicular to the surface) autocorrelation function (FT-DMAF), which includes the following: (1) the effect of temperature on the dynamic motion of the ACAC (b) BC (a) A axis and (2) the effect of the dynamic motion of the ACAC (b) BC (a) A axis on the IR active vibrational modes. [14,15] It is conceivable that this alternate approach to investigating these effects will lead us to more new findings on possible alkyne ACBCACBCA coupling reaction mechanisms on different metal surfaces.…”