Knowledge Bank

Stark spectra for four bands of yttrium hydride in the $19300-19800cm-1$ region have been recorded by exciting the molecules in the presence of external electric field up to 16 kV/cm and monitoring laser induced fluorescence. The molecules have been produced in a free jet molecular beam apparatus by laser vaporizing yttrium metal in the presence of He carrier gas doped with 2 - 5% of $H2$ or $NH3$. Rotational and $\Omega$ quantum number assignments of the bands have been established with the help of Stark effect. The electric dipole moments have been measured to be equal to: $1.569(64)$, $2.325(8)$, $3.316(11)$, $2.273(6)$, and $1.537(8)$ for the $X1\Sigma +$ ground state and the 19385, 19746, 19572, and $19575cm-1$ excited states, respectively. Strong variation of the effective $\Omega$ quantum number with J has been detected for the lowest rotational levels of the $19572cm-1$ state. The effective values have been determined to be equal to $\Omega =1$ (fixed value), $\Omega =1.472(7)$, and $\Omega =1.624(18)$ for $J=1$, $J=2$, and $J=3$, respectively. Possible perturbers of the $19572cm-1$ state will be considered. Electronic character of the ground state and the four excited states will be discussed. Correlation of the dipole moment and the $\Omega$ quantum number in Stark spectroscopic measurements will be analyzed and required experimental conditions for breaking of such correlation will be determined.