INFRARED-SPECTROSCOPY OF HOMOGENEOUSLY NUCLEATED HYDRAZINE AEROSOLS -DISORDERED AND CRYSTALLINE PHASES

Fourier Transform Infrared Spectroscopy has been used to study homogen eously nucleated hydrazine (N2H4) aerosols formed in a variable temper ature flow cell. The spectra contain both resonant absorptions and Mie scattering features which allow detailed information to be obtained o n the phase of the aerosol particles and the size distribution that is formed. In addition, the relative intensities of the absorption and s cattering features can be used as a qualitative probe of the density o f the particles. A disordered phase is observed at cell temperatures r anging from 230 to 180 K and a transition to a crystalline phase occur s over the temperature range 180-175 K. At lower temperatures the infr ared spectra become progressively narrower, indicating that the qualit y of the crystals improves as the temperature is lowered. The result i s previously unobserved details in the hydrazine N-H stretch vibration s of the crystalline solid. The high quality of the spectra obtained u nder these conditions suggests that at the high condensation rates cha racteristic of the present experiments, self-annealing yields highly c rystalline particles. Mie calculations, based upon the complex refract ive index data for amorphous solid hydrazine, are shown to have utilit y in modeling the infrared spectrum of the disordered phase, which we tentatively assign as a supercooled liquid.