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Title: Microhydrated dihydrogen phosphate clusters probed by gas phase vibrational spectroscopy and first principles calculations

We report infrared multiple photon dissociation (IRMPD) spectra of cryogenically-cooled H2PO4-(H2O)n anions (n = 2–12) in the spectral range of the stretching and bending modes of the solute anion (600–1800 cm-1). The spectra cannot be fully understood using the standard technique of comparison to harmonic spectra of minimum-energy structures; a satisfactory assignment requires considering anharmonic effects as well as entropy-driven hydrogen bond network fluctuations. Aided by finite temperature ab initio molecular dynamics simulations, the observed changes in the position, width and intensity of the IRMPD bands with cluster size are related to the sequence of microsolvation. Due to stronger hydrogen bonding to the two terminal P=O groups, these are hydrated before the two P–OH groups. By n = 6, all four end groups are involved in the hydrogen bond network and by n = 12, the cluster spectra show similarities to the condensed phase spectrum of H2PO4-(aq). Our results reveal some of the microscopic details concerning the formation of the aqueous solvation environment around H2PO4-, provide ample testing grounds for the design of model solvation potentials for this biologically relevant anion, and support a new paradigm for the interpretation of IRMPD spectra of microhydrated ions.
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [4] ;  [6] ;  [7] ;  [8]
  1. Chinese Univ. of Hong Kong, Shatin (China)
  2. Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin (Germany); Chinese Academy of Sciences, Dalian (China)
  3. National Supercomputing Center in Shenzhen, Shenzhen (China)
  4. Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin (Germany)
  5. Univ. of California, Berkeley, CA (United States)
  6. Universitat Leipzig, Leipzig (Germany)
  7. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  8. Chinese Univ. of Hong Kong, Shatin and Shenzhen (China)
Publication Date:
OSTI Identifier:
1214438
Grant/Contract Number:
AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
Physical Chemistry Chemical Physics. PCCP (Print)
Additional Journal Information:
Journal Name: Physical Chemistry Chemical Physics. PCCP (Print); Journal ID: ISSN 1463-9076
Publisher:
Royal Society of Chemistry
Research Org:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English