a rotational analysis of the nali a/sup 1/ sigma /sup +/ electronic state is reported. laser-induced fluorescence combined with fourier transform spectrometer was used to record the spectra the analysis has been done by model fitting of the a/sup 1/ sigma /sup +/ state term values excited by fixed kr/sup +/ laser lines and dye laser lines oscillating in the region between 750 nm and 600 nm additional information about the lowest a/sup 1/ sigma /sup +/ state vibrational levels was obtained from the infrared spectra of the b/sup 1/ pi -a/sup 1/ sigma /sup +/ transition induced by fixed ar/sup +/ laser lines in the blue-green region. vibrational levels up to nu '=25 have been observed, allowing the evaluation of accurate spectroscopic constants of the a/sup 1/ sigma /sup +/ state. comparisons with previous experimental and theoretical studies are reported. main molecular constants are given below in cm/sup -1/. t/sub e/=14205.28(3): omega /sub e/=188.0328(9): omega /sub e/ chi /sub e/=0.926(1): b/sub e/=0.2759(3): alpha /sub e/=0.002323(8): d/sub e/=7791(5)