  Intensities in Tm I emission series originating from a common upper level are
measured using a Fourier transform spectrometer. The derived relative
transition probabilities within each series are compared to the theoretical
predictions obtained from large-scale calculations that combine configuration
interaction with many-body perturbation theory. Moreover, the Tm I spectrum
recorded in an external magnetic field is analyzed. Our theoretical results
well describe the current measurements and show no more than a two-fold
difference from previous experimental data on absolute transition
probabilities. Additionally, Land\'e g factors, hyperfine structure constants,
and atomic electric quadrupole moments for several levels of interest are
computed and compared to experimental observations, where available.
