  We report the first survey of molecular emission from cometary volatiles
using standalone Atacama Compact Array (ACA) observations of the Atacama Large
Millimeter/Submillimeter Array (ALMA) toward comet C/2015 ER61 (PanSTARRS)
carried out on UT 2017 April 11 and 15, shortly after its April 4 outburst.
These measurements of HCN, CS, CH$_3$OH, H$_2$CO, and HNC (along with continuum
emission from dust) probed the inner coma of C/2015 ER61, revealing asymmetric
outgassing and discerning parent from daughter/distributed source species. This
work presents spectrally integrated flux maps, autocorrelation spectra,
production rates, and parent scale lengths for each molecule, and a stringent
upper limit for CO. HCN is consistent with direct nucleus release in C/2015
ER61, whereas CS, H$_2$CO, HNC, and potentially CH$_3$OH are associated with
distributed sources in the coma. Adopting a Haser model, parent scale lengths
determined for H$_2$CO (L$_p$ $\sim$ 2200 km) and HNC (L$_p$ $\sim$ 3300 km)
are consistent with previous work in comets, whereas significant extended
source production (L$_p$ $\sim$ 2000 km) is indicated for CS, suggesting
production from an unknown parent in the coma. The continuum presents a
point-source distribution, with a flux density implying an excessively large
nucleus, inconsistent with other estimates of the nucleus size. It is best
explained by the thermal emission of slowly-moving outburst ejectas, with total
mass 5--8 $\times$ 10$^{10}$ kg. These results demonstrate the power of the ACA
for revealing the abundances, spatial distributions, and locations of molecular
production for volatiles in moderately bright comets such as C/2015 ER61.
