An apparatus for studying high resolution overtone spectroscopy on a molecular beam has been constructed. With it molecular overtone lineshapes with dramatically reduced spectral congestion and Doppler broadening can be interrogated. A high sensitivity, low temperature bolometer is used to monitor the energy content of the molecular beam. A continuously tunable narrow band laser source, efficiently amplified in a resonant Fabry Perot cavity through which the molecular beam travels, imparts vibrational energy to the molecules. This is then transferred to the bolometer and therefore gives rise to the spectrum when the frequency is scanned. ▵v = 4 overtones of H2O have been studied. Other molecules have also been considered and will be discussed in terms of the nearby density of dark states.