Knowledge Bank

Using a pulsed Nd:YAG pumped OPO laser, the vibrational predissociation spectra of small polymers of $H2O$, HF, $CH3OH$, and $NH3$ (as well as of the nonhydrogen bonded species $C6H6$ and $C6H$12) were obtained in the wavelength region 2800--4000 $cm-1$. The clusters were formed by expanding the gases through a heated nozzle, then defined by a set of three skimmers. The resulting beam was crossed at $90\circ$ by the laser beam, and the products detected using a rotatable, electron bombardment mass spectrometer. From the frequency dependence of the signal obtained at a fixed detector angle ($4\circ$ from the molecular beam) the dominant process observed is [ (RH){n} +h\nu \longrightarrow RH(v=1) \cdots (RH){n-1} \longrightarrow RH + (RH)_{n-1} ] Where n=3, 4, 5, 6 and R = OH, $CH3O$, H, $NH2$. The velocity distribution of the products gives information on the disposal mechanism of the excess energy and the time scale of the dissociation process. The spectra observed are qualitatively similar to condensed phase and matrix isolated results and suggests the utility of testing intermolecular potentials describing condensed phases with the measured molecules beam spectra.