The growth rates for pure Artin groups of dihedral type

We consider the kernel of the natural projection from the Artin group of dihedral type I 2 ( k ) to the associated Coxeter group, which we call a pure Artin group of dihedral type and write P I 2 ( k ) . We show that the growth rates for both the spherical growth series and geodesic growth series of P I 2 ( k ) with respect to a natural generating set are Pisot numbers.