Line mixing in self- and foreign-broadened water vapor at 6μm

Line mixing has been measured for two pairs of transitions in the ν 2 band of H 2 16 O. The rotational assignments of the four lines (in terms of the rotational quantum numbers J , K a and K c ) are (a) two P branch lines: (1 0 1)←(2 1 2) mixing with (2 1 2)←(3 0 3) at 1539.061 and 1540.300 cm −1 , respectively; and (b) two R branch lines: (3 0 3)←(2 1 2) mixing with (2 1 2) ←(1 0 1) at 1652.400 and 1653.267 cm −1 , respectively. Pressure broadening coefficients of H 2 O (halfwidths, pressure shifts and off-diagonal relaxation matrix elements) are reported for seven broadeners (self, H 2 , He, CO 2 , N 2 , O 2 and air) from retrievals performed by multispectrum fitting implemented with line mixing. The effect is largest for self- and H 2 -broadening.