  We present combined experimental and theoretical results on strong-field
ionization of oriented carbonyl-sulphide molecules by circularly-polarized
laser pulses. The obtained molecular frame photoelectron angular distributions
show pronounced asymmetries perpendicular to the direction of the molecular
electric dipole moment. These findings are explained by a tunneling model
invoking the laser-induced Stark shifts associated with the dipoles and
polarizabilities of the molecule and its unrelaxed cation. The focus of the
present article is to understand the strong-field ionization of
one-dimensionally-oriented polar molecules, in particular asymmetries in the
emission direction of the photoelectrons. In the following article (Phys. Rev.
A 83, 023406 (2011)) the focus is to understand strong-field ionization from
three-dimensionally-oriented asymmetric top molecules, in particular the
suppression of electron emission in nodal planes of molecular orbitals.
