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The dynamics of ionized gas around the W33 Main ultracompact HII region isstudied using observations of hydrogen radio recombination lines and a detailedmultiwavelength characterization of the massive star-forming region W33 Main isperformed. We used the Giant Meterwave Radio Telescope (GMRT) to observe theH167$\alpha$ recombination line at 1.4 GHz at an angular resolution of 10arcsec, and Karl. G. Jansky Very Large Array (VLA) data acquired in the GLOSTARsurvey to study the dynamics of ionized gas. We also observed the radiocontinuum at 1.4 GHz and 610 MHz with the GMRT and used GLOSTAR 4$-$8 GHzcontinuum data to characterize the nature of the radio emission. In addition,archival data from submillimeter to near-infrared wavelengths were used tostudy the dust emission and identify YSOs in the W33 Main star-forming region.The radio recombination lines were detected at good signal to noise in theGLOSTAR data, while the H167$\alpha$ radio recombination line was marginallydetected with the GMRT. The spectral index of radio emission in the regiondetermined from GMRT and GLOSTAR shows the emission to be thermal in the entireregion. Along with W33 Main, an arc-shaped diffuse continuum source,G12.81$-$0.22, was detected with the GMRT data. The GLOSTAR recombination linedata reveal a velocity gradient across W33 Main and G12.81$-$0.22. The electrontemperature is found to be 6343 K and 4843 K in W33 Main and G12.81$-$0.22,respectively. The physical properties of the W33 Main molecular clump werederived by modeling the dust emission using data from the ATLASGAL and Hi-GALsurveys and they are consistent with the region being a relatively evolved siteof massive star formation. The gas dynamics and physical properties ofG12.81$-$0.22 are consistent with the HII region being in an evolved phase andits expansion on account of the pressure difference is slowing down.

A multiwavelength study of the W33 Main ultracompact HII region