Through measurement of the equivalent width (fractional integrated absorption) of collision-broadened lines of the P branch of the HCl fundamental vibration-rotation band at 3.5 μ, the Lorentz half-widths of these lines have been determined and optical collision cross sections deduced therefrom. The cross sections which have been obtained are those for collisions between HCl molecules and Ar, CO2, CO, D2, H2, HBr, He, Ne, N2, O2, as well as other molecules of HCl. One of the more interesting aspects of these cross sections is their dependence on the rotational state of the absorbing molecule and the various forms which this J dependence takes for the different foreign gases. The line widths range between the extremes of 0.233 and 0.0111 cm—1 atmos—1 while the collision cross sections range between 3.04×10—14 and 0.091×10—14 cm2. Also reported are recently measured values of the strengths for the first eight lines of the P branch of the HCl fundamental. The strength of this band based on these measurements has been found to be 143±5 cm—2 atmos—1 at 300°K.

The strengths and self-broadened half-widths of the lines of the fundamental band of HBr have been measured by a curve-of-growth method. The method uses a correction for two overlapping lines recently devised by Sakai. The squares of the electric dipole matrix elements, |M01(m)|2, for the lines have been calculated from the strengths. From the theory of Herman and Wallis and |M01(0)|2, the dipole moment derivative M1 is found to be 0.468×10—10 esu. From the slope at m = 0 of |M01(m)|2 the vibration—rotation interaction parameter, θ, is found to be 1.20. The dependence of the strengths on rotational quantum number J is compared to the J dependence of the strengths of the other hydrogen halides and is compared to theory. A similar comparison is made for the J dependence of the half-widths.

The strengths of the vibration—rotation lines of the first overtone, first hot band, and fundamental band of HBr have been measured by a curve of growth method, applying a correction for two overlapping lines devised by Sakai. The squares of the electric-dipole matrix elements |M02(m) |2 and |M12(m) |2 for the lines have been calculated, and have been fitted, respectively, to a cubic and quadratic polynomial in m, using the method of least squares. The experimental results for all three bands are compared with the theory of Herman and Wallis. The fact that the experimental |M02(0) |2 is less than that calculated from a linear dipole-moment function clearly requires a positive value of M2, the second derivative of the dipole-moment function. The squares of the matrix elements |M01(0) |2 and |M02(0) |2 are used to calculate M1 and M2, the dipole-moment coefficients, for Morse and anharmonic oscillators. Of all the possible sets of M1 and M2 obtained in each case, the one giving results in better agreement with |M12(0) |2 is chosen. The chosen values of the dipole-moment coefficients are M1=+4.56×10−11 esu and M2=+0.69×10−3 esu cm−1 for the Morse oscillator and M1=+4.63×10−11 esu and M2=−0.70×10−3 esu cm−1 for the anharmonic oscillator. Since the sign of M2 is positive, the Morse oscillator results are preferred.

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The performance of a commercial rapid scanning spectrometer was checked experimentally in studies of flash photolysis, photochromism, phosphorescence, and thermal radiation. Rapid scan spectra (1 msec to 100 msec) were measured in portions of the uv, visible, and ir spectral regions (total wavelength coverage 250 nm to 14.5 microm), at rates up to 800 spectra/sec. The effect of grating line spacing on resolution and spectral range was measured. In absorption measurements, successive scans of the background radiation source were photometrically reproducible to within 1 part in 80. The effect of scanning time on resolution was studied experimentally; resolution of 0.94 cm(-1) at 2400 cm(-1) was achieved with signal-to-noise of 30:1, during rapid scanning. Recording on magnetic tape and oscillographic recording are illustrated.