  We report 75As-nuclear magnetic resonance (NMR) and nuclear quadrupole
resonance (NQR) measurements on transition-metal arsenides LaRu2As2,
KCa2Fe4As4F2, and A2Cr3As3. In the superconducting state of LaRu2As2, a Hebel-
Slichter coherence peak is found in the temperature dependence of the
spin-lattice relaxation rate-1/T1 just below Tc, which indicates that LaRu2As2
is a full-gap superperconducor. For KCa2Fe4As4F2, antiferromagnetic spin
fluctuations are observed in the normal state. We further find that the
anisotropy rate RAF = Tc1/Tab1 is small and temperature independent, implying
that the low energy spin fluctuations are isotropic in spin space. Our results
indicate that KCa2Fe4As4F2 is a moderately overdoped iron-arsenide
high-temperature superconductor with a stoichiometric composition. For
A2Cr3As3, we calculate the electric field gradient by first-principle method
and assign the 75As-NQR peaks with two crystallographically different As sites,
paving the way for further NMR investigation.
