COLLISION BROADENING OF TRANSIENT ABSORPTION SPECTRA .I. HYDROXYL LINEWIDTHS IN (0,0) (A-]X) TRANSITION AT LOW TEMPERATURES

The collision broadening cross sections of the OH (0, 0) (A → X) ultraviolet transition have been measured for 14 broadening gases at 293°K and for water vapor at 378°K. They were obtained by applying corrections for Doppler and instrumental broadening to direct width measurements of OH absorption lines in high resolution spectra. The OH was generated by flash photolysis of H2O2 or H2O in an excess of broadening gas. The assumption that the cross section is independent of the OH rotational quantum number J appears valid for all these gases except water, for which it was necessary to assume that the cross section is a decreasing function of J. The collision widths at 293°K and 580 torr range from a low of 0·04 cm-1 for helium to a high of 0·16 cm-1 for hydrogen. For water vapor at 378°K and 546 torr, the collision width varies from about 0·3 cm-1 for J = 1 2; to about 0·06 cm-1 for J = 7 1 2;. The collision widths, when extrapolated to flame temperatures, appear to agree with earlier measurements as well as can be expected. The cross sections obtained are generally larger than those derived from transport property measurements, but all are within a factor of two of the latter values. © 1969.