  Rydberg States are used in our One Atom Maser experiment because they offer a
large dipole moment and couple strongly to low numbers of microwave photons in
a high Q cavity. Here we report the absolute frequencies of the P$_{3/2}$
states for principal quantum numbers $n=36$ to $n=63$. These measurements were
made with a three step laser excitation scheme. A wavemeter was calibrated
against a frequency comb to provide accurate absolute frequency measurements
over the entire range, reducing the measurement uncertainty to 1MHz. We compare
the spectroscopic results with known frequency measurements as a test of
measurement accuracy.
