COMPLEX REFRACTIVE-INDEXES IN THE INFRARED OF NITRIC-ACID TRIHYDRATE AEROSOLS

The refractive indices of nitric acid trihydrate (NAT) have been deter mined from the infrared spectra of laboratory generated aerosols. The aerosols are formed via homogeneous nucleation in a flow cell with sep arate regions for nucleation and observation, allowing for independent control of the temperature conditions in these regions. A spectrum of small, non-scattering particles is recorded to determine the frequenc y dependent imaginary refractive index, within a scaling factor. A sub tractive Kramers-Kronig routine is then used to calculate the real ind ex. The scaling factor for the imaginary indices is determined by fitt ing a spectrum associated with larger, scattering particles, which dep ends on both the real and imaginary portions of the refractive indices . The complex refractive indices of NAT are reported over the range 70 0 cm(-1) to 4000 cm(-1). While in good qualitative agreement with prev iously reported results, there are significant quantitative difference s which are discussed.