In recent years the 6.67 GHz masing transition of CH3OH has proven to be a superior tracer of massive star formation (see Minier 2001). Maser sites often occur in proximity to UCHII regions, however, up to 75 per cent of sites have no detectable radio counterpart (Walsh 1998) and are instead hypothesised to trace the less evolved 'hot molecular core' phase of stellar evolution. This has been confirmed for a only handful of well known sources (e.g., Cesaroni 1994). Presented here are the results of multi-species molecular line observations towards warm, dusty clumps, undertaken with the goal of investigating the relationship between hot cores, UCHII regions and CH3OH masers. Data from the 22-m Mopra telescope is used extensively in this thesis and substantial efforts were made to calibrate the brightness temperature scale. Measurements conducted on SiO masers and planets show that the beam pattern is divided into a Gaussian main beam plus an inner error lobe, which in 2004 contained 1/3 of the power in the main beam. Full-width half-maximum beam sizes were measured from the data and the beam efficiencies were derived for the years 2000-2004. A 3-mm wavelength molecular line survey was conducted, using Mopra, towards 83 massive star-forming clumps associated with CH3OH masers. Emission from the transitions 13CO (1-0), N2H+ (1-0), HCO+ (1-0), HCN (1-0) and HNC (1-0) was detected towards 82 sources (99 per cent), while CH3OH emission was detected towards 78 sources (94 per cent). The warm gas tracer CH3CN was observed specifically to search for hot core chemistry, and was detected towards 58 sources (70 per cent), confirming that CH3OH masers are excellent tracers of hot cores. CH3CN is found to be brighter and more commonly detected towards masers associated with UCHII regions compared to 'isolated' masers. That CH3CN is detected towards isolated maser sources strongly suggests that these objects are internally heated. The molecular line data have been used to derive rotational temperatures and chemical abundances in the clumps and these properties have been compared between sub-samples associated with different indicators of evolution. In particular, CH3OH is found to be brighter and more abundant in UCHII regions and in sources with detected CH3CN, and may constitute a crude molecular clock in single dish observations. Gas-kinematics were analysed via asymmetries in the HCO+ line profiles. Approximately equal numbers of red and blue-skewed profiles, indicative of inward or outward motions, respectively, are found among all classes of object. Bolometric luminosities were derived via greybody fits to the sub-millimetre and mid-infrared spectral energy distributions, and an empirical gas-mass to luminosity relation of L proportional to M^0.68 was fit to the sample. This is a considerably shallower power law than L proportional to M^3 for massive main-sequence stars. In the mid-infrared, 12 sources were identified as 'infrared dark clouds' (IRDCs). Such objects have been hypothesised as precursors to the hot core phase of evolution, however, we find these sources have greater linewidths and rotational temperatures than the bulk of the sample, and one contains an embedded HII region The filamentary star forming region NGC3576 was also investigated via a molecular line and 23 GHz continuum mapping survey, utilising the ATCA, Mopra and Tidbinbilla telescopes. The results of these observations provide detailed information on the morphology, masses, kinematics, and physical and chemical conditions along the cloud. Analysis of NH3 data has revealed that the temperature and linewidth gradients exist in the western arm of the filament. Values are highest near to the central HII region, indicating that the embedded cluster of young stars is influencing the conditions in the bulk of the gas. Six new H2O masers were detected in the arms of the filament, all associated with clumps of NH3 emission. Star formation is clearly underway, however, clump masses range from 1 to 128 solar masses, possibly too low to harbour very massive stars. The lack of detected 23 GHz continuum emission in the arms supports this assertion.

A full-sky free-free template is increasingly important for the high-sensitivity Cosmic Microwave Background (CMB) experiments, such as Planck. On the Galactic plane, where free-free estimations from Halpha measurements become unreliable, Radio Recombination Lines (RRLs) can be used to determine the thermal brightness temperature unambiguously with no dust contamination. RRLs are a powerful tool for the diagnostic of the interstellar medium, tracing the ionised component, its electron temperature, velocity and radial distributions.This thesis describes the investigation of the ionised emission from HII regions and diffuse gas along the Galactic plane using RRLs, with the aim of providing a map of the free-free emission to complement the high latitude Halpha observations. Measuring the free-free emission on the Galactic plane is of great importance to understand and characterise other Galactic emission components: synchrotron, anomalous dust and thermal dust emission. The fully-sampled HI Parkes All-Sky Survey and associated deep Zone of Avoidance Survey are re-analysed to recover extended RRL emission. They include three RRLs (H166alpha, H167alpha and H168alpha) at frequencies near 1.4 GHz. A data cube covering l=20 degree to 44 degree and |b| < 4 degree is constructed of RRL spectra with velocity and spatial resolution of 20 km/s and 14.8 arcmin, respectively. Well-known HII regions are identified as well as the diffuse RRL emission on the Galactic plane.In order to convert the integrated RRL emission into a free-free brightness temperature a value of the electron temperature (Te) of the ionised gas is needed. Using the continuum and line data from the present survey, the variation of Te with Galactocentric radius was derived for the longitude range l=20 degree to 44 degree, with a mean Te on the Galactic plane of 6000 K. The derived Te variation was used to obtain the first direct measure of the free-free brightness in this region of the Galactic plane. Subtraction of this thermal emission from the total continuum at 1.4 GHz leaves the first direct measurement of the synchrotron emission. A narrow component of width 2 degree is identified in the synchrotron latitude distribution.Determining the free-free and synchrotron emission in this region of the Galactic plane identifies the anomalous microwave component, when combined with WMAP and IRIS data. The results are in agreement with models of small spinning dust grains.