  Electronic structure of newly synthesized single crystals of calcium iron
arsenide doped with sodium with Tc ranging from 33 to 14 K has been determined
by angle-resolved photoemission spectroscopy (ARPES). The measured band
dispersion is in general agreement with theoretical calculations, nonetheless
implies absence of Fermi surface nesting at antiferromagnetic vector. A clearly
developing below Tc strongly band-dependant superconducting gap has been
revealed for samples with various doping levels. BCS ratio for optimal doping,
$2\Delta/k_{\rm B}T_{\rm c}=5.5$, is substantially smaller than the numbers
reported for related compounds, implying a non-trivial relation between
electronic dispersion and superconducting gap in iron arsenides.
