  We report detections of atomic species in the atmosphere of MASCARA-2 b,
using the first transit observations obtained with the newly commissioned
EXPRES spectrograph. EXPRES is a highly stabilised optical echelle
spectrograph, designed to detect stellar reflex motions with amplitudes down to
30 cm/s, and was recently deployed at the Lowell Discovery Telescope. By
analysing the transmission spectrum of the ultra-hot Jupiter MASCARA-2 b using
the cross-correlation method, we confirm previous detections of Fe I, Fe II and
Na I, which likely originate in the upper regions of the inflated atmosphere.
In addition, we report significant detections of Mg I and Cr II. The absorption
strengths change slightly with time, possibly indicating different temperatures
and chemistry in the day-side and night-side terminators. Using the effective
stellar line-shape variation induced by the transiting planet, we constrain the
projected spin-orbit misalignment of the system to $1.6\pm3.1$ degrees,
consistent with an aligned orbit. We demonstrate that EXPRES joins a suite of
instruments capable of phase-resolved spectroscopy of exoplanet atmospheres.
