Controlling vibrational excitation with shaped mid-IR pulses

We report selective population of the excited vibrational levels of the ${T}_{1u}$ CO-stretching mode in $\mathrm{W}(\mathrm{CO}{)}_{6}$ using phase-tailored, femtosecond mid-IR ($5.2\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$, $1923\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$) pulses. An evolutionary algorithm was used to optimize specific vibrational populations. Stimulated emission peaks, indicative of population inversion, could be induced. Systematic truncation of each optimized pulse allowed for increased understanding of the excitation mechanism. The pulses and techniques developed herein will have broad applications in controlling ground state chemistry and enhancing vibrational spectroscopies.