Black-body induced ionization rate of Rydberg states in helium

The probabilities of photoionization by the black-body radiation (BBR) were calculated for singlet and triplet S-, P-, and D-Rydberg states of a neutral helium atom. The numerical values obtained on the basis of the Fues model potential for states with the principal quantum number n ranging from 8 to 45 were used to derive a formula which not only reproduces the asymptotical behavior of the ionization rate for n --> infinity, but also describes exactly its maximums. The n-independent constants in this formula are determined by a third order polynomial in powers of the absolute temperature with coefficients derived from the calculated data for the temperature range from 200 to 2000 K.