TOWARD METALLIC HYDROGEN (C)1998 Alan M. Schwartz Chemistry and physics goals are curious to examine and near impossible to achieve, justifying temporally extended large scale academic funding. Metallic hydrogen could be a room temperature superconductor. If it is also metastable (sticks around)... Nobel prize. Failing superconductivity, it would be rocket fuel sporting about five times the specific impulse of liquid hydrogen/oxygen. Liquid hydrogen has a density of 0.07 g/cm^3. Metallic hydrogen at around 0.5 g/cm^3 is seven times denser, plus the energy of compression. Gas giant planets should have metallic hydrogen cores. Ivory tower minds want to know. What is a metal? Metal emerges from insulator when high pressure reduces the energy gap E between the filled valence electron band and the unfilled conduction electron band to kT (k is Boltzmann's constant, T is the absolute temperature). As E nears kT thermal smearing promotes electron probability into the energy gap, a metallic density of electronic states obtains, and the electronic system realizes a Fermi surface characteristic of metal. In the case of hydrogen, each molecule loses an electron free to wander and becomes a diatomic cation. Room temperature compressions suffer because solid hydrogen metallization chokes on crystal structure phase transitions and molecular orientation. Neither exists in a disordered fluid. In 1996 Nellis and Weir shock compressed hydrogen between sapphire plates to 1.4 megabars and 4000 K over 100 nanoseconds to transiently embrace metallic hydrogen (Physics Today 49 17 (1996), Phys. Rev. Let. 76 1860 (1996)). Cornell's Arthur Ruoff squeezed hydrogen to 2.5 megabars in a diamond anvil press at room temperature (no dice), reaching 3.42 megabars in 1998 and still failing metallization. David Ceperley at the National Center for Supercomputing Applications (NCSA) calculated a rigorous theoretical phase diagram for hydrogen. He predicts a first order phase transition solid molecular hydrogen to metallic beginning near 0.5 grams/cm^3 density and minimum 3500 K temperature. The maximum temperature containment of hydrogen in a diamond cell is 230 C. Hydrogen diffuses into the diamond, the atomically densest material known. Deuterium has been shock metallized starting at 0.55 megabar and 8400 C, about 50% more compressible than theory (Science 281 1135,1178 (1998)). This is tremendous fun - destroying ten thousand dollar diamond anvils or blasting 20K liquid deuterium chambers with a 3x10^14 watts/cm^2 laser beam - but it does not fill a vial with a lump or puddle of metallic hydrogen under ambient conditions. How would lowly chemists absent a $billion Nova laser facility give a micron speck of hydrogen squeezed to heaven's gate within a diamond anvil press a good kick upside its electronic head and recover the phase-transformed pieces? A reasonably commonplace laboratory pulsed laser can supply focused transient heating, and the extraordinary thermal conductivity of diamond does the fast quench. There will not be time for hydrogen to diffuse. The trick is to elevate molecular hydrogen's ground state singlet (paired electrons, anti-parallel spins) electronic structure into an excited triplet (unpaired electrons, parallel spins). When one electron/molecule is free to wander, things get interesting. By raising the energy of the ground state we bring metallization that much closer. How do avoid doing something naughty (more heat or pressure) that destroys our diamond anvil cell? We use magnets. Chemical bonds are pairs of electrons with anti- parallel spins. Immerse that conjugal bliss in a sufficiently strong magnetic field and you push to align both spins parallel, progressively raising the energy of the anti-parallel paired state (singlet) until the chemical bond pops open (triplet). Games are already played with molecular hydrogen's nuclear spins. At room temperature the nuclear spins are anti-parallel (low energy, para-hydrogen) or parallel (higher energy, ortho- hydrogen) in a 1:3 ratio, implying an energy gap of about 300 calories/gram (/_\E=-RT(lnK)). Liquid hydrogen at 20K slowly equilibrates to being all low energy ortho isomer. As the heat of vaporization of hydrogen is only 0.11 calorie/gram, you can mysteriously vaporize a whole bunch of stored liquid hydrogen if you do not catalytically equilibrate spin isomers during cooling. Uncle Al proposes repeating Dr. Ruoff's 3 megabar big squeeze on deuterium in an Oxford 20 tesla superconducting magnet's bore. Leave your credit cards in the anteroom, torque down the gems, and beam in a focused Q-switched or cavity-dumped fat pulse from a frequency doubled benchtop Nd:glass laser. Not only is 530 nm much prettier than near infrared, it focuses into a spot with one quarter the area of the infrared version. The deuterium suddenly loosens up to a fluid as its temperature soars, bonding electrons are ripped into anti-bonding pairs by the magnetic field, and as the system goes metallic fast thermal quench freezes it in place. Was that so hard?