  The lifetime of the asymmetric fundamental stretching 2218 cm$^{-1}$
vibration of the anesthetic gas nitrous oxide (N$_2$O) dissolved in octanol and
olive oil is reported. These solvents are model systems commonly used to assess
anesthetic potency. Picosecond time-scale molecular dynamics simulations have
suggested that protein dynamics or membrane dynamics play a role in the
molecular mechanism of anesthetic action. Ultrafast infrared spectroscopy with
100 fs time resolution is an ideal tool to probe dynamics of anesthetic
molecules on such timescales. Pump-probe studies at the peak of the vibrational
band yield a lifetime of $55 \pm 1$ ps in olive oil and $52 \pm 1 ps$ in
octanol. The similarity of lifetimes suggests that energy relaxation of the
anesthetic is determined primarily by the hydrophobic nature of the
environment, consistent with models of anesthetic action. The results show that
nitrous oxide is a good model system for probing anesthetic-solvent
interactions using nonlinear infrared spectroscopy.
