The formidable progress achieved in the research at extreme conditions led to
important discoveries of many unusual and interesting physical and chemical
phenomena. Materials with high compressibility were and still are of particular
interest due to a significant reduction of volume which could result in unexpected
changes of bonding and/or electronic properties. Among highly compressible
materials simple diatomic molecules such as H2, N2, and O2 are particularly
interesting because they form new types of solids at high pressure.
Hydrogen, being the most abundant element in the universe, possesses simple
electronic structure, therefore, the study of hydrogen systems is of special interest.
In the last three decades, there were subsequently explored and described several
high-pressure phases of hydrogen up to 400 GPa. However, there is still a vast
area of unexplained effects, which requires further analysis.
The contributed work discusses Raman experiments in a wide pressure and
temperature range where rotational and lattice phonon excitations have been
measured in the Raman spectrum of solid H2 and D2 at 10, 77, 150 and 300 K
from 2 to 180 GPa and up to 380 GPa at 300 K. Analysis of the Raman spectra
allows to model how the rotational modes change with pressure and temperature
and how the mass scaling laws evolve as the density increases in both hydrogen
and deuterium. Comparison of vibrational frequencies of the isotopes appears to
be extremely useful for estimation of equivalent pressures for both isotopes.
Nitrogen and oxygen are archetypal elements possessing unique features such as
extremely strong triple bond in case of N2 and magnetic moment in O2 . Both
N2 and O2 exhibit rich polymorphism, with additional phases of O2 derived from
its electronic and magnetic properties. N2 /O2 mixtures (for example, 20.9% O2
and 78% N2 mixture is air that we breathe) have been studied up to 12 GPa at
300 K experimentally and explored up to 500 GPa at 0 K theoretically. In the
current project, N2 /O2 molecular systems are examined at 300 K up to 150 GPa.
Rich polymorphism is observed, with seven phases exhibiting drastically different
Raman spectra for concentrations below 45% of O2 and a more stable area with
three phases in the concentration range from 45% to 80% of oxygen at pressures
above 12 GPa. Moreover, characteristic Raman spectra obtained for the mix with
25% O2 after laser heating to approximately 2000 K at 25 and 96 GPa reveals
pronounced peaks indicating the potential formation of new compounds
