Effect of Pressure on the Absorption Edges of Certain Elements

The effect of pressure has been measured on the absorption edges of selenium, arsenic, white phosphorus, red phosphorus, and iodine. In all cases a red shift of the edge (decrease of the energy gap) occurs with increasing pressure. White phosphorus undergoes a transition to the conducting black phase near 30 000 atmos. The change in the gap with pressure for selenium is correctly predicted from conductivity measurements. An extrapolation of the gap to zero indicates that the gaps of these elements will have disappeared below 300 000 atmos. This compares with previous work on sulfur where the estimated pressure for zero gap is 400 000 atmos.