  In the present paper, we study nonresonant corrections for experimental
measurements of the transition frequencies in the helium atom. Having attracted
more attention recently, such effects can make a significant contribution to
experiments based on one- and two-photon atomic spectroscopy. Performing a
theoretical analysis of the measurements of the $2^3S_1-3^3D_1$ transition
frequency based on Doppler-free two-photon spectroscopy and the
$2^3P_{0}-3^3D_{1}$ transition energy based on one-photon spectroscopy, we have
found excellent agreement between the experimental and theoretical data taking
into account the dominant contribution of the nonresonant correction. It is
substantiated that the line profile asymmetry caused by the quantum
interference of fine sub-levels of the $ 3^3D_{J} $ $ (J=1,2,3) $ state can
reach tenths of a megahertz. Thus, previously unaccounted nonresonant
corrections can be a potential source eliminating the imbalance in the study of
helium spectra.
