SYNCHROTRON INFRARED-SPECTROSCOPY AT MEGABAR PRESSURES - VIBRATIONAL DYNAMICS OF HYDROGEN TO 180 GPA

We have developed new techniques for measuring infrared spectra at megabar pressures using synchrotron radiation and applied them to study the Q1(1), Q1(1) + S1(0), and Q(R)(J) vibrational transitions of solid hydrogen to 180 GPa. The frequency difference between the Q1(1) infrared and Raman vibrons increases from 3 cm-1 (zero pressure) to 510 cm -1 (180 GPa), indicating a dramatic increase in intermolecular coupling with pressure. A negative frequency shift is observed for the infrared vibron above 140 GPa. A significant increase in frequency and LO-TO splitting of the lattice phonon is also documented.