# why do we get continuous intensity in spectra?

we know energy levels of a molecule is discrete. So we should get only sharp peaks for any spectra. But in most of the spectra I see a continuous intensity? why is so? In the following spectra the peaks are understood but why the tail of the peaks don't touch zero intensity line?

The spectra are actually always continuous if the resolution in frequency of the spectral analyzer and sensitivity in intensity of the detector is high enough. The spectrum of radiation emitted by hot atomic gases and molecules is called discrete because it has very sharp spectral peaks and looks as if formed of lines. But they are actually peaks with non-zero width $\Delta \omega$ and finite height. This is because the radiation of the atom or molecule is never a perfect sinusoidal wave; rather it consists of many such waves damped down to zero, added with various phases. When such signal is decomposed in to its Fourier components, typically it has non-zero intensity at each frequency.