Knowledge Bank

The $v\prime \prime =0$ progression of the A $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi$ - X $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi$ system of Cl0 has been recorded photoelectrically in the first order of 2400 grooves/mm grating using a 1.26m spectrometer. C10 was generated in a fast flow system at near room temperature and 1.5 mn Hg total pressure. Continuum radiation from a Xe are source was passed back and forth along a lm flow tube by means of an external arrangement of concave mirrors. The line positions for each of the recorded bands ($3\le v\prime \le 12$) were computed from the available constants for the X- and A-$states1$. Absorption cross section profiles for individual bands were then generated from the known Franck-Condon $factors2$ and trial values of temperature, linewidth and band strength. Synthetic absorption profiles for the recorded bands were then obtained readily by convolution with the known triangular slit function. A non-linear least squares routine was applied iteratively to obtain improved estimates of the temperature, linewidth and band strength as well as two additional parameters which served to calibrate the spectra against the known C10 (A - X) wave numbers. The matching of the experimental data and the synthetic absorption profiles is excellent for all bands. A smooth variation of the electronic transition moment with upper state vibrational quantum number has been established. The linewidths are about twice those estimated approximately from photographic plates by Coxon and $Ramsay3$. The parameters obtained in the present work could be used to generate reliable synthetic absorption spectra for the longer wavelength $v\prime \prime =0$ bands under stratospheric conditions. Comparison with experiments data might then provide means for continuous measurement of absolute C10 concentrations in the stratosphere. 1 J. A. Coxon, H. E, Jones and E. G. Skolnik, Can. J. Phys. 54, 1043 (1976). 2 J. A. Coxon, J. PhotoChem. 6, 439 (1976/77). 3 J. A. Coxon and O. A. Ramsay, Can. J. Phys. 54, 1034 (1976)d