C.Weldon Mathews

The emission spectra of H35Cl+, H37Cl+, D35Cl+, and D37Cl+ in the region 2700–4100 Å

Abstract The A 2 Σ + -X 2 Π emission spectrum of HCl+ has been measured and analyzed for four isotopic combinations. These analyses extend previous work and provide rotational constants for the v = 0–2 levels of the ground state and for the v = 0–9 levels of the excited state. RKR potentials have been determined for both states, although the upper state could not be fitted precisely to such a model. Calculated relative intensities based on these potentials demonstrated that the electronic transition moment must change rapidly with lower state vibrational quantum number. Although considerable caution should be exercised in applying the concept of equilibrium constants to the A 2 Σ + state, the following are the best estimates of these constants (in cm−1) for the X 2 Π state of H35Cl+: Be = 9.9406, ωe = 2673.7, Ae = − 643.7, and r e = 1.315 A . For the A 2 Σ + state of H35Cl: Te = 28 628.08, Be ∼ 7.505, ωe ∼ 1606.5, and r e = 1.514 A .

A reexamination of the spin-rotation constant for 2Π states: The A-X band system of HCl+

Abstract Using the line positions measured by Sheasley and Mathews, we have reanalyzed the A 2 Σ + -X 2 Π emission spectrum of H 35 Cl + , H 37 Cl + , D 35 Cl + , and D 35 Cl + employing the Hamiltonians and “direct approach” described by Zare, Schmeltekopf, Harrop, and Albritton. The new values for the molecular constants now show the expected isotope relations. Attention is concentrated on the centrifugal distortion correction to the spin-orbit splitting, A D , and the spin-rotation constant, γ, of the 2 Π state. Fixing A D to values calculated using an algorithm by Coxon, a value for γ is derived. This compares poorly to the value of γ expected from an approximation suggested by Van Vleck. The source for this discrepancy is suggested to be the inadequacy of the Van Vleck approximation for the spin-rotation constant and/or the fact that the experimentally derived value is, in general, only an effective parameter containing both the “true” spin-rotation interaction and pseudo-spin-rotation interactions caused by electronic perturbations, such as simultaneous interaction with 2 Σ + and 2 Σ − states or interactions with 2 Δ or other Λ ≠ 0 states with different multiplicity.

Infrared spectra and isomerization of CHNO species in rare gas matrices

Abstract Infrared and uv absorption spectra of the CHNO isomers in rare gas matrices and their photolysis products by ultraviolet light were studied. The most efficient processes occurring in the matrix involve isomerization between the CHNO species. The NCO free radical is the only fragment appearing in the ir spectrum. The diatomic fragments CN, NH, and OH are also observable in the uv spectrum of photolyzed samples.

Analysis of the 0001 Ã2Σ+-0010 X̃2Π band of 14NCO and 15NCO

Abstract Bands of the A 2 Σ + - X 2 Π i system of NCO have been observed during a study of the flash photolysis of mixtures of HCN and ozonized oxygen and their isotopic modifications. In particular, the 00 0 1 2 Σ + -00 1 0 2 Π i (a) band of 15 NCO has been measured and analyzed, thus providing the first molecular parameters for this isotopic species. From the B values for 14 NCO and 15 NCO, the individual bondlengths, r (NC) and r (CO), are derived for the ground and excited states.

Analysis of the bands of the B2Σ+-X2Σ+ transition in 12C16O+ and 13C16O+

Abstract The First Negative bands of 12 C 16 O + and 13 C 16 O + , in the spectral region 40 000–46 000 cm −1 , have been photographed at a resolution sufficient to resolve the spin-doubled components. These data for 12 C 16 O + , along with previously reported data of the same transitions, as well as microwave transitions of 12 C 16 O + in the ground state, have been explicitly included in a least-squares fit to determine the most precise set of molecular constants to date for the B 2 Σ + and X 2 Σ + states of 12 C 16 O + . Furthermore, we report a rotational analysis of the First Negative bands of 13 C 16 O + for the first time. Several molecular constants characterizing 13 C 16 O + in the B 2 Σ + and the X 2 Σ + states, including spin-doubling parameters, have been determined.

The resonance fluorescence of BO2 excited by a pulsed dye-laser

Abstract The fluorescence spectra of BO 2 excited by a continuously tunable pulsed laser provided about fifty newly-assigned transitions. These transitions confirm and extend earlier vibrational assignments involving the X 2 II and A 2 II states.

The electronic states of carbon monofluoride: Low-lying valence states

Abstract Multiconfiguration Hartree-Fock calculations are reported on the low-lying valence states, the X2Π, 4Σ−, B2Δ, and 2Σ± states, of carbon monofluoride. The wavefunctions describe dissociation of the molecule to the correct atomic limits and take account of the atomic 2s-2p near-degeneracy effect. For the ground state the calculations give (with experimental values in parentheses): a bond length of 1.286 A (1.2667 A), a fundamental frequency of 1292 cm−1 (1308 cm1), and a dissociation energy of 3.93 eV (5.5 ± 0.1 eV). A 4Σ− state arising from the C ( 3 P) + F ( 2 P) manifold is calculated to lie just 2.66 eV above the ground state. The B2Δ state, calculated adiabatic excitation energy 6.59 eV (6.12 eV), is found to dissociate to C ( 1 D) + F ( 2 P) via a potential maximum. Calculations are also reported on a repulsive 2Δ state arising from ground state atoms.

The ultraviolet absorption spectrum of HCNO in the gas phase

Abstract A gas-phase absorption spectrum of fulminic acid (HCNO and DCNO) has been observed between 2440 and 2850 A. The spectrum consists of a single progression of headless bands separated by about 345 cm −1 . Although no discrete rotational structure could be detected, the spectrum is interpreted in terms of a transition from the linear (or nearly linear) ground state to a nonlinear excited state.

The rotational spectrum of HCNO in excited bending combination states

Abstract Millimeter wave rotational transitions of HCNO have been measured and assigned for 25 different sublevels in the vibrational states v1v2v3v4v5 = 00004, 00012, 00013, 00021, 00022, and 00101. The measurements extend to 252 GHz covering J values up to J = 11 ← 10. Accurate effective constants Beff and Deff were obtained for all of these levels. Each state was treated separately, because of the quasilinearity of the ν5 mode, and the lines were analyzed in terms of an effective Hamiltonian for linear molecules. Several Coriolis-type resonances between levels with adjacent l values were found. One set of resonances, analogous to that found earlier for lower levels, could be analyzed. Fits to the effective Hamiltonian were unsatisfactory in reproducing some of the measured frequencies, indicating resonances which were not analyzed, but the constants obtained show the trend in the parameters of the effective Hamiltonian as a function of bending excitation.

The electronic states of carbon monofluoride: Rydberg states

Abstract Hartree-Fock and multiconfiguration Hartree-Fock calculations are reported on some low-lying Rydberg states of CF and the ground state of CF + . For the CF + ground state, 1 Σ + , the calculations give a bond length of 1.55 A, a fundamental frequency of 1821 cm −1 , and a dissociation energy of 6.9 eV. Many interactions between the valence and Rydberg state manifolds are revealed. Also a strong mixing of the 3 dσ and 4 sσ components due to an accidental degeneracy is described.