The existence and stability of the linear hydrogenic chain { H } _ { 3 } and H _ { 2 } ^ { - } in a strong magnetic field is established .
Variational calculations for { H } _ { 3 } and H _ { 2 } ^ { - } are carried out in magnetic fields in the range 10 ^ { 11 } \leq B \leq 10 ^ { 13 } G with 17-parametric ( 13-parametric for H _ { 2 } ^ { - } ) , physically adequate trial function .
Protons are assumed infinitely massive , fixed along the magnetic line .
States with total spin projection S _ { z } = -3 / 2 and magnetic quantum numbers M = -3 , -4 , -5 are studied .
It is shown that for both { H } _ { 3 } and H _ { 2 } ^ { - } the lowest energy state corresponds to M = -3 in the whole range of magnetic fields studied .
As for a magnetic field B \gtrsim 10 ^ { 11 } G both { H } _ { 3 } and H _ { 2 } ^ { - } exist as metastable states , becoming stable for B \geq 1.9 \times 10 ^ { 11 } G and for B \geq 2.7 \times 10 ^ { 11 } G , respectively .
The excited states ^ { 4 } ( -4 ) ^ { + } , ^ { 4 } ( -5 ) ^ { + } of { H } _ { 3 } and H _ { 2 } ^ { - } appear at magnetic fields B > 7 \times 10 ^ { 11 } and 10 ^ { 12 } G , respectively .