Fractional factorial design and principal component analyses are applied to CH3F vibrational harmonic frequencies and infrared intensities from density functional calculations. Five effects for 16 wave functions of a 2(5-1) fractional factorial design are investigated: the kinds of exchange (S or B) and correlation (VWN or LYP) functional; the valence basis set (6-31G or 6-311G) and the level of diffuse and polarization functions supplementing this basis set. The main effects on the frequencies are related to modifications of both the exchange and correlation functionals. For the intensities main effects are related to the exchange functional and to the level of polarization functions used. Principal component analysis indicates that for wave functions used in the 2(5-1) factorial design those including the B exchange and VWN correlation functionals are the best ones for estimating the harmonic frequencies of CH3F. For the infrared intensities a wave function including the B exchange functional and a basis set supplemented by (3df, 3pd) polarization functions provides the most accurate CH3F results. The calculated frequency results were significantly improved by use of a B3LYP functional with a 6-311 valence, (3df, 3pd) polarization and ++ diffuse function basis set. However several calculations with the BLYP functional provided more accurate infrared intensity estimates than those with the B3LYP functional. (C) 1998 Elsevier Science B.V. All rights reserved.546831841