Permanent electric dipole signature in molecular frame photoelectron momentum distribution of H₂O

We theoretically investigate the process of single-photon single ionization of H₂O by a linearly polarized few-cycle attosecond XUV pulse with the goal of answering the question on whether a permanent electric dipole of bent molecule such as H₂O has an imprint in its photoelectron momentum distribution (PMD). While the investigation of photoionization involving H₂O has been done before [1]-[5], these investigation focus either on angular distributions or on time delays in molecular photoionization. Using the $R$-matrix with time dependence method, we compute the PMD of H₂O for the attopulse's propagation directions of $\hat{x}$, $\hat{y}$ and $\hat{z}$ in the molecular frame where $\hat{z}$ axis correspond to the C₂ axis. In each case, we extract the PMD for when the dipole of the molecule is pointing along the $+\hat{z}$ and $-\hat{z}$. An asymmetry map is computed to quantify the asymmetry of the PMD due to the electric dipole imprint. We found that an asymmetry is shown in the PMD when the propagation axis of the attopulse is in the direction where the lone pairs of H₂O molecule are in plane with the polarization plane. This study provides a potential application of dipole signatures mapping using attosecond pulses for bent molecules.