The characteristic transition of the NV- centre at 637 nm is between
3A2 and 3E triplet states. There are also
intermediate 1A1 and 1E singlet states, and the
infrared transition at 1042 nm between these singlets is studied here using
uniaxial stress. The stress shift and splitting parameters are determined, and
the physical interaction giving rise to the parameters is considered within the
accepted electronic model of the centre. It is established that this
interaction for the infrared transition is due to a modification of
electron-electron Coulomb repulsion interaction. This is in contrast to the
visible 637 nm transition where shifts and splittings arise from modification
to the one-electron Coulomb interaction. It is also established that a dynamic
Jahn-Teller interaction is associated with the singlet 1E state,
which gives rise to a vibronic level 115 cm−1 above the
1E electronic state. Arguments associated with this level are
used to provide experimental confirmation that the 1A1 is the
upper singlet level and 1E is the lower singlet level.Comment: 19 pages, 6 figure