Emission spectra and electronic structure of group IIIa monohalide cations

Abstract

Optical spectra of ten AX+ ions (A=B, Al, Ga, In; X=F, Cl, Br) have been observed in the visible and near UV; a total of 18 band systems were newly discovered. The emission was produced by chemiluminescent reactions A++X2 at low (2–10 eVCM) kinetic energy in a beam-gas arrangement. A position-sensitive photon counting detector with large surface area and very low dark count rate was employed, the resolution was mostly 5–50 Å FWHM. Three types of band systems were observed: (1) For all AX+ combinations except BCl+ and BBr+, a very broad quasicontinuum with undulatory structure appears. On the basis of electronic state correlation arguments, photoelectron data, some ab initio calculations and, in one case, a known emission spectrum (InCl+) these band systems were identified as B 2Σ+–X 2Σ+ transitions. It is concluded that the excited state potentials are considerably displaced against the ground state, and their energetics are given. (2) For six species AX+, narrow band systems were observed in the 2500 Å region. They could be clearly identified as being due to C 2Π–X 2Σ+ transitions by means of comparison with the systematics of the analogous A 2Π–X 2Σ+ transitions of the isoelectronic alkaline earth halides, by the resolved fine structure, and, in the case of AlF+, by an ab initio calculation. (3) In the GaCl+, GaBr+, and InBr+ spectra, narrow features accompany the C–X transitions. They are attributed to D 2Σ+–X 2Σ+ transitions, analogous to the alkaline earth halide B 2Σ+–X 2Σ+ band systems. Qualitative electronic state correlations are discussed, and the expected dominant configurations in different regions of the AX+ ground and excited states are given. These are in accord with recent ab initio results on AlF+.

Extensive theoretical studies on the low‐lying electronic states of indium monochloride cation, InCl+

“…The computed bond length and vibrational frequency are, respectively, 2.332 Å and 327.9 cm −1 . Its adiabatic excitation energy is calculated to be 39,290 cm −1 , being closer to that of the C 2 Π 3/2 state (40,112 cm −1 ) rather than that of the C 2 Π 1/2 state (37,936 cm −1 ) 8. This is because the scalar relativistic π orbital mimics more π 3/2 than π 1/2 .…”

“…This can be seen clearly from Figure 1. The D 2 Σ + state as termed by Glenewinkel–Meyer et al8 is the third 2 Σ + state of InCl + . Its excitation energy has not been measured experimentally.…”

“…Some weak bands between 320 and 335 nm were also obtained. In 1988, a new C 2 Π state with two Ω components of 1/2 and 3/2 was observed by Glenewinkel–Meyer et al,8 and an unobserved D 2 Σ + state was also suggested. Moreover, two band systems in the regions of 390–410 and 246–251 nm, which were once regarded as the spectra of the InCl molecule,9, 10 were pointed out to be the transitions B 2 Σ − X 2 Σ,7 and C 2 Π 3/2 − X 2 Σ of InCl + , respectively 3…”

In Search of Molecular Ions for Optical Cycling: A Difficult Road

“…In fact, it has been shown that C 2 Π → A 2 Π emission is completely absent in many monofluoride cations AF + (A = B, Al, Ga, In), in contrast to other monohalides, where B = Cl and Br. 87 We therefore examine the prospects of the C 2 Π → X 2 Σ + transition for optical cycling in AlCl + , Our calculations show that the vertical excitation energy to C 2 Π is relatively high (4.7-5.2 eV) and is significantly above the ground-state dissociation limit (Table IV). However, the change in the equilibrium A-Cl bond is relatively small, with the largest value of 0.040 A corresponding to AlCl + .…”

Theoretical spectroscopic studies of InI and InI+

“…The energy separation, 2 3/2 -2 1/2 of the InI + ion corresponds to nearly two thirds of the 2 P 3/2 -2 P 1/2 separation in atomic iodine. Glenewinkel-Meyer et al [23] generated electronically excited ions of the fluorides, chlorides, and bromides of group IIIA. A large number of band systems in the visible and UV region was reported for some of the MX + (X = F, Cl, Br) ions.…”