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

Line mixing has been measured for two pairs of transitions in the ν2 band of H216O. The rotational assignments of the four lines (in terms of the rotational quantum numbers J, Ka and Kc) 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 H2O (halfwidths, pressure shifts and off-diagonal relaxation matrix elements) are reported for seven broadeners (self, H2, He, CO2, N2, O2 and air) from retrievals performed by multispectrum fitting implemented with line mixing. The effect is largest for self- and H2-broadening.