The absorption coefficients of the Q branch of the &ngr;4 band of ClONO2 at 780 cm-1 have been measured over a sample pressure range of 0.1 to 0.4 torr using a tuneable diode laser spectrometer. The peak absorption coefficients derived from these measurements are 1.98(42)¿10-18 cm2 mol-1 at 296 K, and 2.98(47)¿10-18 cm2 mol-1 at 210 K. These are in good agreement with those determined previously by Fourier transform spectroscopy once corrections for the resolution of the instruments are made. Band contour analysis of the &ngr;4+&ngr;6-&ngr;6 and &ngr;4+2&ngr;9-2&ngr;9 bands of 35ClONO2 has been carried out and the results incorporated in the fitting of the observed spectrum. At 213 K the integrated intensity of the theoretical spectrum calculated for the range of identified bands is 6.4¿10-18 cm-1 mol-1. The derived integrated intensity of this whole band system is 8.6¿10-18 cm-1 mol-1, assuming all transition moments of the contributing bands are identical. For the 296 K spectrum of the &ngr;4 system a value of 3.9¿10-18 cm-1 mol-1 is obtained, with a value of 8.4¿10-18 cm-1 mol-1 if all populated states are included. The differences between the integrated intensities of the theoretical spectrum and of the band system are associated with the ''continuum'' contributed by the large number of weak bands associated with thermally populated states. The values obtained for the band systems may be compared with those derived by Ballard et al. <1988> over the range 750 to 830 cm-1 for the entire &ngr;3/&ngr;4 system, and by Davidson et al. <1987> over the range 750 to 791 cm-1. These were 2.09¿10-17 cm-1 mol-1 at 213 K and 3.04¿10-17 cm-1 mol-1 at 296 K for the entire &ngr;3/&ngr;4 system, and 8.1¿10-18 cm-1 mol-1 at 223 K and 12.9¿10-18 cm-1 mol-1 at 296 K. ¿ American Geophysical Union 1996