  Molecular lines are powerful diagnostics of the physical and chemical
properties of the interstellar medium (ISM). These ISM properties, which affect
future star formation, are expected to differ in starburst galaxies from those
of more quiescent galaxies. We investigate the ISM properties in the central
molecular zone of the nearby starburst galaxy NGC 253 using the ultra-wide
millimeter spectral scan survey from the ALMA Large Program ALCHEMI. We present
an atlas of velocity-integrated images at a 1".6 resolution of 148 unblended
transitions from 44 species, including the first extragalactic detection of
HCNH$^+$ and the first interferometric images of C$_3$H$^+$, NO, HCS$^+$. We
conduct a principal component analysis (PCA) on these images to extract
correlated chemical species and to identify key groups of diagnostic
transitions. To the best of our knowledge, our dataset is currently the largest
astronomical set of molecular lines to which PCA has been applied. The PCA can
categorize transitions coming from different physical components in NGC 253
such as i) young starburst tracers characterized by high-excitation transitions
of HC$_3$N and complex organic molecules (COMs) versus tracers of on-going star
formation (radio recombination lines) and high-excitation transitions of CCH
and CN tracing PDRs, ii) tracers of cloud-collision-induced shocks
(low-excitation transitions of CH$_3$OH, HNCO, HOCO$^+$, and OCS) versus shocks
from star-formation-induced outflows (high-excitation transitions of SiO), as
well as iii) outflows showing emission from HOC$^+$, CCH, H$_3$O$^+$, CO
isotopologues, HCN, HCO$^+$, CS, and CN. Our findings show these intensities
vary with galactic dynamics, star formation activities, and stellar feedback.
