Ion association in aqueous solutions probed through vibrational energy transfers among cation, anion, and water molecules

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review

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Author(s)

  • Jiebo Li
  • Hongtao Bian
  • Hailong Chen
  • Bryan T. Hoang
  • Junrong Zheng

Detail(s)

Original languageEnglish
Pages (from-to)4274-4283
Journal / PublicationJournal of Physical Chemistry B
Volume117
Issue number16
Publication statusPublished - 25 Apr 2013
Externally publishedYes

Abstract

KSCN and NH4SCN aqueous solutions were investigated with intermolecular vibrational energy transfer methods. In a KSCN/H2O (1/10 molar ratio) solution, 90% of the initial excitation of the CN stretch (∼2066 cm-1) of the SCN- anion is transferred to the HOH bending mode (∼1636 cm-1) of water molecules with an energy transfer time constant 3.1 ps. In a NH4SCN/H2O (1/10 molar ratio) solution, only 49% of the CN excitation flows to the water HOH bending mode with a time constant 6.3 ps. Most of the remaining CN excitation goes to the NH bending mode (∼1460 cm-1) of the NH+ cation with a time constant of 7.0 ps. The results indicate that about 50% of the energy transfer channel from the CN stretch to the HOH bending observed in the KSCN solution is overpowered by the NH4+ cations in the NH4SCN/H2O solution. Ion concentration dependent measurements support this argument. According to the dipole/dipole approximation, the CN/OH energy transfer occurs most efficiently between SCN- anions and the water molecules closest to them. The experimental results therefore suggest that more than 50% of the water molecules closest to the SCN- anions are replaced by the NH4+ cations in the NH4SCN/H2O (1/10 molar ratio) solution. The percentage is much larger than the NH4+/water ratio of 10%, indicating that the ion association between NH4+ and SCN- is caused by the chemical nature of the solution rather than the statistical "forced contact" because of the high ion concentration. © 2012 American Chemical Society.

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Citation Format(s)

Ion association in aqueous solutions probed through vibrational energy transfers among cation, anion, and water molecules. / Li, Jiebo; Bian, Hongtao; Chen, Hailong; Wen, Xiewen; Hoang, Bryan T.; Zheng, Junrong.

In: Journal of Physical Chemistry B, Vol. 117, No. 16, 25.04.2013, p. 4274-4283.

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review