Vibrational and rotational relaxation times of solvated molecular ions

M. Li, J. Owrutsky, M. Sarisky, J. P. Culver, A. Yodh, R. M. Hochstrasser

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Abstract

Infrared pump-probe and infrared polarization spectroscopy have been used to measure the vibrational relaxation times (T1) of the antisymmetric stretching mode and the reorientation times (TR) for N 3 -, NCS-, and NCO- in D2O and/or mettianol. For N3 -, experiments were also conducted in H2O and hexamethyl-phosphamide (HPMA) solutions. The rapid vibrational relaxation and slow reorientation observed demonstrate strong coupling between the ions and the solvents. Longer vibrational relaxation and shorter reorientation times measured for NCS- reveal weaker solvent interactions that may be due to the importance of the charge distribution and the form of the normal coordinate. A comparison of the T1 and T R times in different solvents permits a determination of the relative interaction strengths for the solvents investigated. The relatively weaker coupling of N3 - in the aprotic solvent HMPA demonstrates the importance of hydrogen bonding in strong solvent interactions in ionic solutions. The experimental results are compared with recent molecular dynamics simulations of ionic solutions.

Original languageEnglish
Pages (from-to)5499-5507
Number of pages9
JournalThe Journal of Chemical Physics
Volume98
Issue number7
DOIs
StatePublished - 1993

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