Analysis of the behaviour of confined molecules using ² H T ₁ nuclear magnetic relaxation dispersion

Abstract

A four-site exchange model is developed in order to explain deuterium T 1-nuclear magnetic relaxation dispersion (NMRD) profiles of acetonitrile in silica pore systems. The four-site exchange model comprises a bulk, surface and two types of burried or cavity sites. It is found that the residence time of acetonitrile-d 3 at a flat Si-surface is less than 100 ps. No bilayer-like ordering of acetonitrile is formed at the Si-surface because no quadrupole splitting was observed. The dispersion in the deuterium T1-NMRD profiles are due to relatively few so-called β-sites with molecular residence time in the range 0.2-2 micro seconds. This deuterium T 1-NMR dispersion experiment suggest that the retention time of different analysts can be studied in terms of their residence time in β sites.