A 1.3,cm spectral line study of the W33 region

At a distance of 2.4,kpc, W33 is one of the most prolific sources of molecular line emission, and it is an excellent research target for a centimeter spectral line search. We carried out a 1.3,cm spectral line survey in the frequency range 18--26,GHz. The lines we identified include 44 radio recombination lines (RRLs) and 24 molecular lines, excluding transitions from the main isotopolog of NH_3. The RRLs are associated with the ionized gas from W33,Main. Intensity ratios between RRL pairs with varying differences in the principal quantum number n,(i.e., Δ n) from the same element at adjacent frequencies agree with ratios expected under conditions of local thermodynamical equilibrium. In spite of a resulting helium-to-hydrogen abundance ratio (equal emitting volumes assumed) of (10.7±1.8)%, which is consistent with expectations, helium shows broader turbulent line widths than hydrogen. The difference amounts to a few kilometers per second, hinting that the spatial distributions are slightly different. The molecular lines are attributed to nine different species (CH_3OH, HC_3N, SiS, c-C_3H_2, CH_3CN, NH_2D, HNCO, H_2O and CCS). Rotation temperatures and column densities were derived from CH_3OH transitions using rotational temperature diagram analysis. Maser emission produced by water vapor and methanol have been observed in W33,Main, W33,A, and W33,B. Our survey discovered a CH_3OH,(10_2,8--10_1,9,E) maser in W33,Main. Toward W33,B1, the fractionated deuterium-to-hydrogen ratio (D/H) deduced from para-NH_2D/NH_3 is estimated to be łesssim(1.0,±,0.2)times10-3. For the other molecular W33-hotspots, 3σ$ upper limits are -3 . At linear scales of (0.5,pc), fractional abundances and excitation temperatures do not reach values close to those in well-established hot cores, but higher-resolution measurements may alter this picture.