  We measure electron and nuclear spin transition frequencies in the ground
state of nitrogen-vacancy (NV) centers in diamond for two nitrogen isotopes
($^{14}\mathrm{NV}$ and $^{15}\mathrm{NV}$) over temperatures ranging from 77 K
to 400 K. Measurements are performed using Ramsey interferometry and direct
optical readout of the nuclear and electron spins. We extract coupling
parameters $Q$ (for $^{14}\mathrm{NV}$), $D$, $A_{||}$, $A_{\perp}$,
$\gamma_e/\gamma_n$, and their temperature dependences for both isotopes. The
temperature dependences of the nuclear-spin transitions within the $m_s = 0$
spin manifold near room temperature are found to be +0.52(1) ppm/K for
$^{14}\mathrm{NV}$ ($|m_I=-1> \leftrightarrow |m_I=+1>$) and -1.1(1) ppm/K for
$^{15}\mathrm{NV}$ ($|m_I=-1/2> \leftrightarrow |m_I=+1/2>$). An isotopic shift
in the zero-field splitting parameter $D$ between $^{14}\mathrm{NV}$ and
$^{15}\mathrm{NV}$ is measured to be $\sim$ 120 kHz. Residual transverse
magnetic fields are observed to shift the nuclear spin transition frequencies,
especially for $^{15}\mathrm{NV}$. We have precisely determined the set of
parameters relevant for the development of nuclear-spin-based diamond quantum
sensors with greatly reduced sensitivity to environmental factors.
