  An analytical representation for the potential energy curve for the ground
state $X^1\Sigma^+$ of the hydrogen fluoride molecule (HF) is presented in the
frame of the Born-Oppenheimer approximation. The analytical expression for the
potential energy curve is based in a two point Pad\'e approximant which
correctly reproduces the asymptotic behaviors at small $R\rightarrow 0$ and
large $R\rightarrow\infty$ internuclear distances, obtaining not less than 4-5
s.d. when compared with experimental results. The rovibrational spectra of the
diatomic molecule HF is calculated by solving the Schr\"odinger equation for
nuclear motion. The ground state $X^1\Sigma^+$ contains 21 vibrational states
($\nu,0$) and 722 rovibrational states ($\nu,L$). A slight modification in the
differential equation for nuclear motion allows us to obtain the rovibrational
spectrum of the ground state of the deuterium fluoride (DF) and tritium
fluoride (TF) molecules. Full spectra is presented for this two isotopologues
species of HF.
