  We study the eigenvalues of the Kohn Laplacian on a closed embedded strictly
pseudoconvex CR manifold as functionals on the set of positive oriented
pseudohermitian structures $\mathcal{P}_{+}$. We show that the functionals are
continuous with respect to a natural topology on $\mathcal{P}_{+}$. Using an
adaptation of the standard Kato--Rellich perturbation theory, we prove that the
functionals are (one-sided) differentiable along 1-parameter analytic
deformations. We use this differentiability to define the notion of critical
pseudohermitian structures, in a generalized sense, for them. We give a
necessary (also sufficient in some situations) condition for a pseudohermitian
structure to be critical. Finally, we present explicit examples of critical
pseudohermitian structures on both homogeneous and non-homogeneous CR
manifolds.
