set A (r_c 1.971): c = 2641.9 m/s at 373.0 K, P = -0.0580 GPa;  set B (r_c 1.986): c = 2699.5 at 367.6 K, P = +0.0270
at 371 K: P(A) = -0.0602, P(B) = +0.0307 GPa;  dP/dr_c = 6.06 GPa/bohr, dc/dr_c = 3840 m/s per bohr
zero pressure at r_c = 1.9809 bohr;  speed at 371 K and zero pressure: 2678.5 m/s (+5.8% on 2,531; +6.8% on 2,508.5)
