Lambda-type doubling parameters for molecules in Π electronic states of triplet and higher multiplicity

Lines in the b3Σ+-a3II and c3Σ+-a3II systems of AlF show partially resolved hyperfine structure. This structure has been attributed to magnetic interactions involving the 27Al nucleus for which I = 5/2. About twenty unblended lines from the (0, 0) bands of the two systems have been analysed in detail, using a computer programme to simulate the profiles by calculating the frequencies and intensities of individual hyperfine transitions. For low values of the rotational quantum number, the lines show a simple triplet structure, which reflects the case (bβS) coupling in the 3Σ states. Analysis of these lines gives values for the Fermi contact parameters in the two states involved (bF = 0.049 cm-1 and 0.057 cm-1 in the b3Σ+ and c3Σ+ states respectively). As the rotational quantum number increases, the hyperfine patterns become less regular, indicating a departure from case (bβS) coupling in the 3Σ states and from case (aβ) coupling in the 3II state. By reproducing the details of these line-shapes, it has also proved possible to determine values for the electron spin-spin and spin-rotation parameters in the two 3Σ states: b3Σ+ λ = -0.025(10)cm-1 γ = 0.0000(3)cm-1 c3Σ+ λ = 0.00(1)cm-1 γ = 0.0015(10)cm-1 The experimental values for the Fermi contact parameter of AlF in the a3II and b3Σ+ states are well produced by a simple single configuration molecular orbital calculation but the value for the c3Σ state is rather larger than expected on this basis.

An Analysis of Hyperfine Interactions in the Electronic Spectrum of AIF

The feasibility of laser cooling AlH and AlF is investigated using ab initio quantum chemistry. All the electronic states corresponding to the ground and lowest two excited states of the Al atom are calculated using multi-reference configuration interaction (MRCI) and the large AV6Z basis set for AlH. The smaller AVQZ basis set is used to calculate the valence electronic states of AlF. Theoretical Franck–Condon factors are determined for the A1Π → X1Σ+ transitions in both radicals and found to agree with the highly diagonal factors found experimentally, suggesting computational chemistry is an effective method for screening suitable laser cooling candidates. AlH does not appear to have a transition quite as diagonal as that in SrF (which has been laser cooled) but the A1Π → X1Σ+ transition transition of AlF is a strong candidate for cooling with just a single laser, though the cooling frequency is deep in the UV. Furthermore, the a3Π → X1Σ+ transitions are also strongly diagonal and in AlF is a practical method for obtaining very low final temperatures around 3 μK.

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Electronic states and spin-forbidden cooling transitions of AlH and AlF

Supersonic molecular beam samples of iridium monocarbide IrC and iridium mononitride IrN were generated using a laser ablation/reaction source and characterized using high resolution (Δν<30 MHz FWHM) laser induced fluorescence spectroscopy. This is the first identification of gaseous IrN. Numerous strong band systems in the 18 800 to 14 360 cm−1 spectral range were assigned as the (v′,0) progression of the A 1Π–X 1Σ+ band system of IrN. The (1,0) and (0,0) bands were analyzed to produce a set of fine and hyperfine parameters. The electric field induced effects on the R(0) line of these bands were analyzed to produce permanent electric dipole moments: A 1Π(v=0) 2.78(2) D, A 1Π(v=1) 2.64(2) D, X 1Σ+(v=0)=1.66(1) D. The (0,0) band of the D2 Φ7/2−X 2Δ5/2 system of IrC was recorded and analyzed to produce a set of fine and hyperfine parameters. The electric field induced effects on the R(2.5) branch feature were analyzed to produce permanent electric dipole moments: D 2Φ7/2(v=0) 2.61(6) D and X 2Δ5/2(v=0) 1.60(7) D. Plausible electronic configurations consistent with the experimental observations are given.

The optical and optical/stark spectrum of iridium monocarbide and mononitride

Fourier transform spectroscopy of VO: Rotational structure in the A4Π-X4Σ− system near 10 500 Å

The a3Π-X1Σ+ transition of AlF has been observed in absorption by heating a mixture of AlF3 and Al powder to approximately 1 600 K in a King type furnace. The position of the Q2 head of the a3Π-X1Σ+ (0, 0) band is found to be 27 254.1 cm-1 or 3 668.13 A, which is in good agreement with the value of the singlet-triplet separation determined from earlier perturbation analysis. The (0, 0) and (1, 1) bands have been rotationally analyzed. The following equilibrium values of constants (in cm-1) have been determined for the a state: Te = 27 239.4 (1) ωe = 830.3 (3) ωexe = 4.6 (2) Be = 0.55718 (3) αe = 0.00468 (5)

C Malmberg

Papers

An Analysis of Hyperfine Interactions in the Electronic Spectrum of AIF

Rotational Analysis of the a3Π-X1Σ+ Transition of AlF