Effects of high pressure on molecules.

Recent high-pressure studies reveal a wealth of new information about the behavior of molecular materials subjected to pressures well into the multimegabar range (several hundred gigapascal), corresponding to compressions in excess of an order of magnitude. Under such conditions, bonding patterns established for molecular systems near ambient conditions change dramatically, causing profound effects on numerous physical and chemical properties and leading to the formation of new classes of materials. Representative systems are examined to illustrate key phenomena, including the evolution of structure and bonding with compression; pressure-induced phase transitions and chemical reactions; pressure-tuning of vibrational dynamics, quantum effects, and excited electronic states; and novel states of electronic and magnetic order. Examples are taken from simple elemental molecules (e.g. homonuclear diatomics), simple heteronuclear species, hydrogen-bonded systems (including H2O), simple molecular mixtures, and selected larger, more complex molecules. There are many implications that span the sciences.