Thousands of unknown water vapor weak lines in the spectral region between 13200 and 2270 cm-1 are deduced from extrapolations of experimental results. These lines are then included in the HITRAN database and used in line-by-line calculations of atmospheric opacity with standard atmospheric profiles. The weak lines predicted by a theoretical model are also used in the line-by-line model to estimate their contribution to the absorption of solar radiation. The additional absorption of solar radiation is of order 1.5 to 2.5 W/m2 at 45 mm precipitable water, about 8.5% to 14% of the absorption due to HITRAN lines in the spectral region. The effect is also compared with that of a continuum model. ¿ 1999 American Geophysical Union