The ultrafast dynamics of HBr–water clusters: Influences on ion-pair formation

Abstract

The ultrafast dynamics of HBr–water clusters have been investigated using pump–probe spectroscopy coupled with reflectron time-of-flight mass spectrometry. HBr clusters, mixed HBr–water clusters, and protonated water clusters are observed in the mass spectra. Dynamic studies reveal that when an HBr chromophore of a cluster with less than five solvent molecules is excited electronically, solvent reorganization occurs to form the solvent separated ion-pair [S. M. Hurley et al., Science 298, 202 (2002)]. The present paper focuses on the influence of clustering on the dynamics of the C and D states of HBr. In addition, further evidence is presented which confirms that complete dissolution of HBr requires five solvent molecules in the isolated species found in complexes comprised of pure water or HBr/H2O mixtures.

Atmospheric processes on ice nanoparticles in molecular beams

“…Large amount of attention has been paid to the photochemistry of hydrogen halides in water clusters due to their relevance to the ozone depletion process (Hurley et al, 2002 , 2003 ; Dermota et al, 2005 ). Photodissociation in clusters has been also investigated for other relevant species, e.g., OClO (Fenner et al, 1997 ; Kreher et al, 1999 ), and nitric acid (Li and Huber, 2001 ).…”

Mass spectrometry of aerosol particle analogues in molecular beam experiments

“…Small HX(H 2 O) N clusters represent the ideal system to pursuit this question. Femtosecond pump‐probe spectroscopy showed that N = 5 water molecules were needed to generate the contact ion pair in HBr‐water clusters . Both HCl and HBr in water clusters were investigated by FTIR spectroscopy suggesting the acidic dissociation in the range of N = 3‐5 .…”

“…Femtosecond pump-probe spectroscopy showed that N = 5 water molecules were needed to generate the contact ion pair in HBr-water clusters. 258,259 Both HCl and HBr in water clusters were investigated by FTIR spectroscopy suggesting the acidic dissociation in the range of N = 3-5. 260,261 Essentially the same size range for acidic dissociation could be obtained from comprehensive IR-UV experiments and theoretical investigations of small HCl and water clusters by Reisler and Bowman reviewed recently.…”

Acid Dissociation in (HX)n(H2O)n Clusters (X = F, Cl, Br, I; N = 2, 3)

“…pKas for dissociation in aqueous environments, bond lengths in Å, and dipole moments in Debyes (Cotton and Wilkinson, 1988;Weast et al, 1989;Sato and Hirata, 1999). Microsolvation studies of a single acid molecule with one or more water molecules have expanded our understanding of acid dissociation and, in some cases, have pinpointed 4 the number of solvent molecules needed to achieve the formation of the ion pair (Laasonen and Klein, 1994;Schindler et al, 1994;Lee et al, 1996;Ando and Hynes, 1999;Conley and Tao, 1999;Gertner et al, 1999;Cabaleiro-Lago et al, 2002;Devlin et al, 2002;Hurley et al, 2003;Voegele and Liedl, 2003;Kuo and Klein, 2004;Odde et al, 2004;Gutberlet et al, 2009;Vargas-Caamal et al, 2016a). These studies correspond to ideal situations that do not account for crucial factors such as increasing acid concentration via the explicit addition of new molecules.…”