Diode-laser measurements of linestrength and temperature-dependent lineshape parameters for H2O transitions near 1.4 μm using Voigt, Rautian, Galatry, and speed-dependent Voigt profiles

Linestrengths and lineshapes for 7 H2O absorption transitions in the nu(1) +nu(3) combination band near 1.4 mu m were measured at high resolution using tunable diode laser absorption. H2O- and N-2-perturbed lineshapes were measured at 300-1300 K and 2-760 Torr and Voigt, Galatry, Rautian, and quadratic-speed-dependent-Voigt profiles were least-squares fit to measured spectra using a multi-spectrum fitting routine. Transitions with J '' of 6-18 were studied to highlight the importance of collisional resonance and illustrate how the best-fit lineshape parameters varied with J ''. The accuracy of the Voigt profile decreased as J '' increased (especially for J=K-c doublets). For transitions in N-2, the collisional-broadening temperature exponents varied from approximate to 0.8 to -0.4 (for the Voigt profile) as J '' increased and this behavior coincided with increasing speed-dependent collisional-broadening coefficients. The quadratic-speed-dependent Voigt profile was found to offer the best combination of accuracy and robust lineshape parameters; however, Rautian and Galatry profiles provided similar performance. (C) 2014 Elsevier Ltd. All rights reserved.