W. S. Felps

Molecular Rydberg states. VII. Water

The optical absorption spectra of H2O and D2O are reported at various pressures for 2000?λ?950 A. The 1670 A band is vibrationally structured (ν2 bend) and the excited 1B1 state contains a considerable intravalence 4a1 component. The 1280 A state 3sa1; 1A1 is linear and dominantly Rydberg. A Renner–Teller analysis of the 1280 A band leads to detection of a perturbing state at 1365 A which may be assigned as a bent, heavily Rydberg 3sa1; 1B1 state. A reanalysis of K‐shell excitation spectra bolsters this 3sa1; 1B1 assignment. Isotope shift studies in the 1130–980 A region lead to some vibronic reassignments. The terminal state of the 968 A absorption band is a linear 5sa1; 1A1 state. In sum, a total of 21 electronic states, comprising fragments of six Rydberg series, have been assigned.

Molecular Rydberg states. XI. Quantum defect analogies between molecules and rare gases

The s and d Rydberg series of hydrogen iodide and methyl iodide are reported. These series are assigned using analogies to the corresponding series in xenon. It is shown that a comparison between molecular spectra and pertinent atomic data provides a facile assignment technique for molecular Rydberg spectra. Using the phase amplitude method, the Rydberg data are analyzed in an attempt to provide information on the residual atomic and molecular potentials and to categorize them qualitatively as attractive/repulsive, long range/short range. It is shown that, for l?2, the centrifugal barrier inhibits ingress of the Rydberg electron into the core and that the molecule is effectively spherically symmetric.

Spin uncoupling in the 6s Rydberg states of methyl iodide. Rotational subband structure in one‐photon absorption

Molecular constants of electronic states, all origins as well as some vibronic bands, derived from the lowest‐energy Rydberg configuration of methyl iodide, are reported. Values of the internal angular momentum parameter ζeff, which is a measure of the strength of Coriolis and vibronic coupling, indicate that the spin of the Rydberg electron is effectively uncoupled from the molecular axis in the pure electronic states and that dynamic interactions between electronic, rotational, and vibrational motions completely quench the internal angular momentum in some vibronic levels. It is concluded that the parameters ζeff, as obtained from one‐photon absorption spectra, are approximately those of the alternate levels, 2E3/2 and 2E1/2, of the CH3I+ ion‐core ground configuration X.

Density effects on high‐n molecular Rydberg states: CH3I and C6H6 in H2 and Ar

The absorption spectra of high‐n Rydberg states of methyl iodide and benzene perturbed by varying number densities of hydrogen or argon, range 0.9×1020–10.5×1020 cm−3 for H2 and 0.6×1020–7.5×1020 cm−3 for Ar, have been investigated. The high‐n molecular states of both absorbers were found to shift linearly with the number density of atomic Ar and molecular H2 scatterers. The Fermi formula modified by the Alekseev–Sobel’man polarization term provides an excellent fit of the shift data. The electron scattering lengths obtained are: 0.93 a0 for H2 and −1.63 a0 for Ar using the CH3I absorber; and 0.99 a0 for H2 and −1.57 a0 for Ar using the C6H6 absorber. The electron scattering lengths for H2 and Ar agree with the results of an empirical model that correlates scattering lengths and the polarizabilities α(spherical) for inert atoms and α2(nonspherical) for H2 molecule.

Molecular Rydberg transitions. XVIII. Vibronic doubling in methyl iodide

A massive vibronic coupling (dynamic Jahn–Teller) effect has been observed in the first s‐Rydberg transition of CD3I. The effect is conditioned more by energy‐denominator (i.e., near degeneracy) sizes than by matrix element (i.e., 〈H′〉?15 cm−1) sizes. The effect is observed in four different transitions of CH3I and CD3I where, by virtue of energy‐denominator variations, alterations of the effect by 2–3 orders of magnitude are observed and interpreted. A very simple model of the coupling is developed and is shown to be numerically powerful. Since the vibronic coupling takes place in an (Ωc,ω)‐spin–orbit coupling regime, the smallness of 〈H′〉 is surprising. It is shown that this small magnitude of 〈H′〉 is attributable to spin‐selection breakdown which the vibronic coupling in question must accomplish even in the (Ωc,ω) regime.

Molecular Rydberg transitions. XX. Vibronic doubling in alkyl bromides

A doubling of absorption bands occurs in certain transitions associated with first s‐ and p‐Ryderg excitations in C2H5Br and C3H7Br. No such doubling occurs in the first d‐Rydberg or second s‐Rydberg excitation of C2H5Br. Furthermore, doubling is not evident in any Rydberg transition of CH3Br, CD3Br, or C2D5Br. The interpretation of this doubling phenomenon invokes vibronic coupling between Rydberg states of the same configuration. The active vibration is a C–H stretching mode ??3000 cm−1 and the presence of doubling is determined by coincidence (or near coincidence) of the intraconfigurational splitting and the frequency of the active vibrational mode.

Molecular Rydberg transitions: Cyanogen chloride☆

Abstract The electronic absorption spectrum of cyanogen chloride has been investigated in the range 2200-1250 A. The first s -Rydberg transitions, X 1 Σ + → 3 Π 1 and X 1 Σ + → 1 Π 1 have been assigned, and analyzed to yield exchange and spin-orbit coupling parameters. The relative intensities of these two transitions have been shown to accord with an intermediate coupling situation. The π → π ∗ intravalence excitations, leading to 1.3 (Σ − , Δ and Σ + ) states, have been discussed. It has been shown that one or both of the 1 Σ − and 1 Δ states have bent geometries and that the 1 Σ + state is located (tentatively) at 79 755 cm −1 . Two σ → π ∗ π → σ ∗ states have been assigned, one at 56 340 cm −1 , the other at 74 450 cm −1 . The latter assignment is tentative, being largely based on observed vibronic interferences between the X 1 Σ + → 1 Π 1 transition and the 74 450 cm −1 transition. A considerable amount of vibrational oscillator strength and quantum defect data is presented.

Molecular Rydberg transitions. The π → 4s transition of CICN

Abstract The first s-Rydberg transition of cyanogen chloride is discussed from the point of view of effective quantum numbers, oscillator strengths and the parameters of an intermediate-coupling model. It is shown that the ratio of oscillator strengths f (X → B)/ f (X → C) could be as low as 10 −2 and, on this basis, a set of first s-Rydberg assignments is proposed for CICN.

Molecular Rydberg transitions. XVI. MCD of CH3Br

Magnetic circular dichroism, first derivative (of absorption), and absorption spectra of methyl bromide are presented for the first s–Rydberg transition region, 55 000–61 000 cm−1. A straightforward analysis in terms of the ratios (MCD/derivative) of the signal amplitudes yields a unique identification of the first s–Rydberg states, 3E(1) and 1E(1). These identifications, in conjunction with oscillator strength ratios and an intermediate coupling model, lead to an assignment of the remaining first s–Rydberg states 3E(2) and 3E(0±). All of these assignments are corroborative of ones based on vibrational analyses and extrapolations [S. Felps, P. Hochmann, P. Brint, and S. P. McGlynn, J. Mol. Spectrosc. 59, 355 (1976)]. The power of MCD techniques in VUV Rydberg analyses is strikingly demonstrated.

Magnetic circular dichroism of CD3I in the vacuum ultraviolet

The magnetic circular dichroism (MCD) of CD3I is reported in the 48 700–60 100 cm−1 region. This region embraces the 5p → 6s manifold, much of the 5p →6 p manifold, and perhaps some members of the 5p → 5d Rydberg manifold of states. The results in the 5p →6 s manifold are confirmatory of the same work in CH3I [Scott et al., J. Chem. Phys. 68, 4678 (1978)]; some questions occur concerning the conferral of absorption intensity on the highly forbidden 5p →6 s[1] state of these molecules. The MCD of part of the 5p →6 p manifold of CD3I is also reported. Five possible 5 p→6 p origins have been securely identified and a sixth has been tentatively assigned. Apart from one of these, that at 58 930 cm−1, the other five origins assigned here match none of those found by MPI spectroscopy [Dobber, Buma, and de Lange, J. Chem. Phys. 99, 836 (1993)], suggesting a degree of complementarity of both data sets. Relative magnetic moments for all six observed states in the 5p → 6p region have been determined: the 58 930 cm−1...