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.
|Number of pages||9|
|Journal||The Journal of Chemical Physics|
|State||Published - 1993|