We report observations and analyses of bands in the spectra of the ArH and ArD molecules due to emission from the 4fRydberg complexes. For ArD, the observed bands are 4f→ 5sand 4f→ 3dλ for all three components λ = 0, 1, and 2 of the 3dstate. These give direct information on all 14 spin–orbit components of the 4fcomplex. For ArH, the data is more limited because the levels of the 5sstate are broadened by predissociation, and only the λ = 2 component of the 4f→ 3dλ transitions is seen clearly, although a number of lines could be assigned to the 4f→ 3dπ band, which is strongly overlapped by the 6s→ 4pband. The 4fcomplexes of both isotopes are good example of Hund's case (d) coupling. The 4forbitals are essentially non-core-penetrating, so that spin–orbit coupling is negligible for them, and the zero–rotation splitting agrees well with calculations from the ab initio quadrupole moment and anisotropic polarizability of the core. The orbit–rotation coupling parameter ξ4fgives a value of the core electric dipole moment that is in reasonable agreement with ab initio and previous experimental values. A summary of the presently known states of ArH and ArD is presented.

We report and rotationally analyze new spectra of the ArH and ArD molecules corresponding to the 0–0 vibrational bands of electronic transitions from thendandnsstates to the 4pRydberg complex, in united atom notation. In ArD, our observation of the 3dδ state, along with previous observations of the 3dπ and 3dσ states, demonstrates that the components of the 3dstate are widely separated and can be treated as Hund's case (b) states, unlike the components of thenpand 4fstates, which form closely coupled case (d) Rydberg complexes. The band 4dσ → 4phas also been assigned. The 4dπ component is known from previous work of Lipson, but as yet the 4dδ component is unknown. Emission from the 6sand 8sstates is also analyzed. From the intensities in the rotational structure, there is evidence that the 6sstate interacts with the 3dσ state. In ArH, we analyze the 0–0 bands of the 3dπ → 4p, 3dδ → 4p, 4dσ → 4p, and 6s→ 4ptransitions. Unlike the rotational levels of the 5sstate, which are heavily broadened by predissociation, the 4plevels of ArH are sharp, so we can perform a more accurate and detailed analysis for this isotope than was possible previously. Qualitative features of the ArH spectra essentially mirror those of ArD, except that emission from the 3dσ state was not identified, possibly due to a perturbation particular to this isotope.

The complete rotational analysis of the 4f(2Φ,2Δ,2Π,2Σ+)→4d 2Δ (6600 cm−1), 4f(2Φ,2Δ,2Π,2Σ+)→4d 2Π (8500 cm−1), and 4d 2Δ→5p 2Π (7100 cm−1) Rydberg electronic transitions of KrD is reported. The two newly observed states, the doublet 4f complex and 4d 2Δ together with the np(2Π,2Σ+), nd 2Σ+, ns 2Σ+, and nd 2Π studied earlier by Dabrowski et al., [Mol. Phys. 63, 269 (1988)], and by Dabrowski and Sadovskiı́ [Mol. Phys. 81, 291 (1994)], form a set of states which permits the whole Rydberg electronic structure of the molecule to be determined from the experimental data.

characterized the n = 2 and the n = 3 Rydberg states, the lowest bound states of the molecule. Only the isotopomers H3 and D3 were considered in detail. The spectra of the triatomic molecule were observed in the cathode glow of a hollow cathode discharge, superimposed on the spectra of the diatomic molecule. In fact the lines of the triatomic were distinguishable from those of the diatomic only because they did not occur in the anode glow. The study of the two other isotopomers, H2D and HD2, did not appear promising at that time. Spectra taken with a mixture of isotopes simultaneously produced lines of H3, D3, H2, HD, D2, as well as a few of H2D and HD2. A new development arose when we began to study the spectra of the rare gas hy­ drides [6-8] by means of an afterglow tube of a design similar to that of Cossart [9]. We found to our surprise that when argon was used as the exciting gas to which H2 was added, a very clean spectrum of H3 was obtained without any superimposed H2 lines. ArH spectra were also observed but were in general much less intense, and could be eliminated completely by varying the experimental conditions. Figger et at. [10-13] have been able to observe the emission spectra of each separate isotopomer by neutralization of mass-selected ion beams. However, their spectra were not obtained under high resolution, nor did they attempt any rotational analysis of the mixed isotopes. We considered it therefore to be worthwhile to study the spectra of H2D and HD2. The 6025 A band was chosen since it has the simplest rotational structure and because the lines are fairly sharp for all the isotopomers. New spectra taken on our Bomem Fourier Transform Spectrometer permitted us to improve the accuracy of the earlier measurements on H3 and D3, as well as to obtain fairly complete new data on H2D and HD2. At the same time more careful measurements of linewidths were possible. The object of the present paper is to report the results of these studies.

The ground electronic state of argon hydride has a repulsive potential apart from a long-range van der Waals minimum, but the Rydberg excited states have bound potentials similar to those of the ion ArH+. These states can be described approximately in terms of united-atom quantum numbers nl. We report here rotational analyses of the bands 5p-->5s, 5p-->6s, and 6p-->5s of ArD, which help to further characterize the np Rydberg series. In ArH the bands 5p-->5s and 6p-->5s have broad lines because of predissociation in the lower state, and 5p-->6s is difficult to analyze without further information. The present data are fitted with a Hund's case (d) effective Hamiltonian. In previous work the 4p state was found to have a very small sigma-pi splitting, but this does not hold for the higher np states, and is probably due to an accidental cancellation between electrostatic and polarizability contributions. On the other hand, the spin-orbit coupling decreases monotonically with n. Features of the rotational levels are discussed in terms of the high-J limiting quantum numbers l(J)=N-R and s(J)=J-N, where R=N+, in particular the effect of spin-orbit coupling on the levels with (l(J),s(J)) =(-1,1/2) and (0,-1/2), which produces a tendency to Hund's case e behavior in 4p, and a sharp avoided crossing in 6p. The corresponding avoided crossing in 5p would occur beyond the present range of observed J values.

$^{1}$ J. W. C. Johns, J. Mol. Spectrosc. 36, 488-510 (1970). $^{2}$ R. H. Lipson, Mol. Phys. 65, 1217-1225 (1988). $^{3}$ I. Dabrowski, G. DiLonardo, G. Herzberg, J. W. C. Johns, D. A. Sadovskii, and M. Vervloet, J. Chem. Phys. 97, 7093-7110 (1992).

The 23 920 cm-1, 21 950 cm-1, and 17 840 cm-1 emission bands of KrD have been analysed successfully as transitions from the 8p, 7p, and 6p Rydberg complexes to the lowest bound state, 2Σ. It was found that the structure of these states corresponds to a special case of l uncoupling with a Coriolis-like linear dependence of the case (d) electron-rotation energies on the quantum number R. The structure of the lowest member of the series, the 5p(2Σ, 2Π) complex, has been obtained from the simultaneous analysis of the 5 050 cm-1 and 5 800 cm-1 emission bands as transitions from the 4d2Π case (b) upper state to the 5p2Σ and 5p2Π components of the complex. The latter are widely split, E Π - E Σ = 735 cm-1, due to electronic interactions and are further distorted by strong spin-orbit interactions. The 5p(2Σ, 2Π) complex corresponds to the p complex of ArD studied recently by Dabrowski, I., Dilonardo, G., Herzberg, G., Johns, J. W. C., Sadowskii, D. A., and Vervloet, M., 1992, J. chem. Phys., 97, 7093.

The precise determination of the energy of the EF state of D2 by Gilligan and Eyler (Phys. Rev. A, in press) makes it possible to determine the ionization potential of D2 with an accuracy comparable to that of H2. For this purpose improved wavenumbers for a number of emission bands in the visible and near infrared regions have been obtained. Together with the previously measured 6h-5g, 5g-4f, and 4f-3d transitions the ionization potential is obtained and found to agree extremely well (to 3 parts in 107) with the theoretical value derived from D0(D2+) and D0(D2) (Wolniewicz and Orlikowski, Mol. Phys. 74, 103–111 (1991), and Kolos et al., J. Chem. Phys. 84, 3278–3283 (1986)).

Three fairly strong emission bands of ArD at 6100, 6900, and 10 200 cm−1 have been studied at high resolution. They show very different structures: the first exhibits only Q-form branches, the second P, R, O, and S-form branches, and the third Q, S, and O-form branches. The rotational analysis of each of these bands is not trivial, mainly because the upper state of the first which proved to be also the lower state of the second and third is strongly affected by l uncoupling [i.e., transition to Hund’s case (d)] and as a result the usual method of combination differences cannot be applied in their analysis. However, more sophisticated combination differences have been found between the three bands which lead to unambiguous assignments of rotational quantum numbers and thus to rotational constants. It was found that the upper state of the 6100 cm−1 band can be most conveniently represented as a p(2Σ,2Π) complex. This assumption, together with the theoretical selection rules for such a case, led to a full understanding of the structure of the three bands.

Author Institution: Herzberg institute of Astrophysics, National Research Council of Canada

The 5g–4 f Rydberg groups of H2 and D2 first studied in paper I have been obtained with a tenfold increase in resolution which made it possible to resolve the singlet from the triplet components. As a result we can now establish separately precise values for the energy levels in the triplet and singlet systems. For this purpose we have remeasured a number of transitions between the lower energy levels for which at present only old measurements are available. In particular we obtain accurate values for the energies of the lowest (stable) triplet state a3Σ+g relative to the singlet ground state, as well as of the ionization potential. The values obtained for the former are more accurate than obtained from singlet–triplet anticrossings while the latter are of similar accuracy as those reported recently by McCormack et al. [Phys. Rev. A 39, 2260 (1989)] and fit well within this accuracy with the most recent ab initio values.

A group of lines accompanying the first line of the Pfund series of the H atom has been observed by Fourier transform infrared spectrometry. The lines are due to transitions in molecular hydrogen of a nonpenetrating Rydberg electron possessing a high-orbital angular momentum, which is coupled only loosely to the vibrations and rotations of the H+2 core. Lines belonging to the 6h–5g and 6g–5f (v=0–3) transitions of H2 have been identified. The identifications are based on a calculation of the spectrum from first principles by multichannel quantum defect theory. The interaction between the nonpenetrating electron and the core was evaluated in terms of the permanent and induced molecular moments of H+2 as calculated by Bishop and collaborators. The analogous transitions in D2 have also been observed and assigned.

Extensive emission bands of KrH and KrD have been observed in the near infrared, visible and ultraviolet regions. Most of them can readily be arranged in Rydberg series with nsσ, npσ, npπ, nd and nf upper states and a 5sσ 2Σ lower state. There is a strong resemblance of the diagram of electronic states of KrH to that of the electronic states of the united atom Rb. The present paper deals with the electronic transitions of KrH and KrD corresponding to the 2 S and 2 P states of Rb. Difficulties (not yet entirely overcome) arise with the nd and nf complexes which will be discussed in later papers of this series. The present paper deals only with the 2Σ and 2Π states arising from ns and np orbitals. The conventional molecular constants have been determined. For most electronic states only v = 0 levels have been observed but in a few cases also v = 1 and v = 2 have been observed from hot bands. No bands with v′ ≠ v″ have been found and thus no reliable vibrational frequencies are obtained. The rotational constants of KrH are very similar in value to those of KrH+ as is to be expected for Rydberg states. As for ArH the line widths of the band lines of KrH involving the lowest 2Σ state is not negligible (0·5 cm-1) indicating predissociation in this 2Σ state. This predissociation is presumably caused (as in ArH) by interaction with the repulsive ground state arising from ground state Kr + H. It is however distinctly less strong than in ArH. Indeed in KrD (unlike ArD) line broadening by predissociation is undetectable. NRCC No. 28540. NRCC No. 28540. Notes NRCC No. 28540.