Rotational analysis and deperturbation of the A 2Π → X 2Σ+ and B′ 2Σ+ → X 2Σ+ emission spectra of MgD

- Magnesium monohydride is an important molecule in astrophysics.
- High resolution emission spectra of MgD radical have been analyzed.
- The A 2Π → X 2Σ+ bands of MgD with v′ = 2 and v′ = 3 were rotationally assigned.
- Local perturbations were observed in the A 2Π and B′ 2Σ+ excited states of MgD.
- Off-diagonal electronic matrix elements were determined from a deperturbation analysis.

High resolution Fourier transform emission spectra of MgD radical were analyzed, and the A 2Π → X 2Σ+ bands with v′ = 2 and v′ = 3 were rotationally assigned. Several local perturbations were observed in the A 2Π and B′ 2Σ+ excited states of 24MgD, and a deperturbation analysis was carried out using an appropriate Hamiltonian matrix containing off-diagonal terms connecting the vibrational levels of the two states. Dunham coefficients and band constants were determined for the A 2Π and B′ 2Σ+ states, along with off-diagonal parameters. The equilibrium vibrational constants ωe and ωexe have been determined to be 1155.040(6) and 16.764(4) cm−1, respectively, for the A 2Π state, and 598.108(11) and 6.394(8) cm−1, for the B′ 2Σ+ state. The equilibrium Mg-D distances were found to be 1.67819(3) Å and 2.59355(2) Å for the A 2Π and B′ 2Σ+ states, respectively. RKR potential curves were constructed for the A 2Π and B′ 2Σ+ states, and vibrational radial overlap integrals were computed for the perturbed levels. The off-diagonal matrix elements coupling the electronic wavefunctions of the A 2Π and B′ 2Σ+ states were determined independently for MgD to be a+ = 18.9 ± 0.2 cm−1 and b = 0.694 ± 0.005, in excellent agreement with those for the MgH isotopologue.

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