  We present a density functional theory parametrized hybrid k$\cdot$p tight
binding model for electronic properties of atomically thin films of
transition-metal dichalcogenides, 2H-$MX_2$ ($M$=Mo, W; $X$=S, Se). We use this
model to analyze intersubband transitions in $p$- and $n$-doped $2{\rm H}-MX_2$
films and predict the line shapes of the intersubband excitations, determined
by the subband-dependent two-dimensional electron and hole masses, as well as
excitation lifetimes due to emission and absorption of optical phonons. We find
that the intersubband spectra of atomically thin films of the 2H-${MX_2}$
family with thicknesses of $N=2$ to $7$ layers densely cover the infrared
spectral range of wavelengths between $2$ and $30\ {\rm \mu m}$. The detailed
analysis presented in this paper shows that for thin $n$-doped films, the
electronic dispersion and spin-valley degeneracy of the lowest-energy subbands
oscillate between odd and even number of layers, which may also offer
interesting opportunities for quantum Hall effect studies in these systems.
