where, for the coordinate, q j , the HO i (q j ) are the normalized Harmonic oscillator basis functions, HO i (q j ) = N sc i .H i-1 (x j (q j )) • exp[-1 2 x j (q j ) 2 ]. x j (q j ) is the scaled and shifted coordinate, x j (q j ) = sc j • (q jq j re f ), N sc j i is a normalization factor and H i-1 (x) are the Hermite polynomials. re f is the value of q j at the equilibrium geometry and the expression of sc j is given by 4 k j /G jj where k j and G jj are, respectively, the curvature and the value of contravariant component of the metric tensor at the q re f geometry . The values of the q j re f , sc j and G jj are given in Table for all studied isotopologues.