W. H. Breckenridge

The structure of several electronic states of the Hg–Ar complex as determined by laser double resonance in a supersonic jet

The electronic states of the Hg–Ar complex have been studied in a supersonic free jet expansion using a laser double resonance technique. Detailed observations were made of the states correlating with the mercury 6 3P levels 3P0, 3P1, and 3P2. The states correlating with the 3P0 and 3P2 metastable states had not been studied previously since they are optically inaccessible from the ground state. A model was developed which accounts for the structures of the various states. The binding energies can be related simply to the average orientation of the 6p mercury orbital with respect to the internuclear axis. In addition, the Hg(7 3S1)–Ar Rydberg state was reinvestigated and shown conclusively to exhibit a double minimum potential, with a deep well similar to the Hg–Ar+ ion and a shallow van der Waals minimum at larger internuclear distances.

Mo/ller–Plesset perturbation theory for van der Waals complexes bound by electron correlation effects: Ground states of the Ar and Mg dimers

We demonstrate that MPPT through fourth order is suitable for studying van der Waals correlation‐bound complexes provided that (a) accurate calculations are carried at the SCF level; (b) efficient basis sets for intersystem correlation effects (i.e., dispersion) are used; and (c) the full counterpoise (CP) method is applied to correct for basis set superposition error (BSSE). Interaction potentials are obtained for Ar2 and Mg2 with extended basis sets that contained up through the f‐symmetry functions. For Ar2 the potential is characterized by R≈7.3 a0 and De∼0.34 mhartree and for Mg2 by Re≈7.4a0 and De∼2.1 mhartree. The discrepancies between our potentials and the most accurate semiempirical and experimental results (Ar2:Re∼7.1a0, De ≈0.45 mhartree; Mg2:Re≈7.35a0, De∼1.93 mhartree, are analyzed in detail and attributed to the lack of higher than f‐symmetry functions, as well as, in the Mg2 case, to the approximate nature of the MP4 approach.

Spectroscopic characterization of the lowest singlet states of CdNe, CdAr, and CdKr

We report the characterization of the first excited singlet states of CdNe, CdAr, and CdKr, which correlate with Cd(5s5p 1P1) and the ground‐state rare‐gas atoms. The van der Waals molecules were created in a free jet supersonic expansion and studied by laser‐induced fluorescence, dispersed fluorescence, laser pump/probe action spectra, and spectral simulations. The C 1Π1 states are found to be more strongly bound than their triplet counterparts: 116Cd20Ne (De=89 cm−1, ωe=23.36 cm−1, ωexe=1.80 cm−1, re =3.61±0.05 A); 116Cd40Ar (De=544 cm−1, ωe=47.97 cm−1, ωexe=1.11 cm−1, re=3.28±0.05 A); 114Cd84Kr (De=1036 cm−1, ωe=56.72 cm−1, ωexe=0.81 cm−1, Δre(C 1Π–X 1Σ+) =1.16 A). This is attributed to spatial differences between the atomic p orbital of the singlet vs the triplet excited state of the Cd atom. The D 1Σ0+ states of CdAr and CdKr were found to be repulsive for Franck–Condon accessible internuclear distances. No production of Cd(5s5p 2PJ) states from predissociation of any C 1Π1 molecular state was observed.

Nascent internal energy distributions of MgH(MgD) produced in the reaction of Mg(3s3p1P1) with H2(D2)

Nascent rotational quantum‐state distributions of MgH(v=0,1) and MgD(v=0) have been determined for the reactions Mg(1P1)+H2→MgH+H, Mg(1P1)+D2→MgD+D. The distributions are bimodal, with the major components (∼90%) peaking at very high rotational quantum numbers and the minor components at approximately N=10. The MgH(v=1)/MgH(v=0) ratio is 0.7±0.2, and there is decreasing population in the higher vibrational levels. The ‘‘high‐N’’ distribution is discussed in terms of energy release from bent MgH2 configurations resulting from preferential ‘‘side‐on,’’ insertive attack of H2 by Mg(1P1). This is shown to be consistent with ab initio calculations of the relevant MgH2 potential surfaces. The deconvoluted high‐N distribution for MgD(v=0) is closer to phase‐space‐theory predictions than is that for MgH(v=0), and it is suggested that HMgH and DMgD intermediates are formed with lifetimes nearly long enough for internal randomization of vibrational energy to occur. The minor ‘‘low‐N’’ component could well be due to...

Excitation spectra on CdNe, CdAr, and CdKr molecules in a supersonic jet

Abstract Laser excitation spectra of the van der Waals molecules CdNe, CdAr, and CdKr have been obtained in free-jet supersonic expansions of cadmium vapor in the respective pure rare gases. Analysis of the spectra has yielded spectroscopic constants and dissociation energies of the ground state ( 3 0 + ) and two excited states ( 3 0 + , 3 1) which dissociate asymptotically to Cd(5p 3 P 1 ) atoms.

Reaction of O(1D) with CO2 at Low Temperatures

When O3 dispersed in a solid CO2 matrix, or a mixture of O3 and CO2 dispersed in solid argon is photolyzed using ultraviolet light, O3 disappears and a new substance forms. This substance shows infrared‐absorption maxima at 2053, 1894, 1070, 975, and 564 cm−1. These absorption bands are ascribed to CO3. The molecule CO3 is capable of reacting with O2 to form O3. Experiments using 18O‐labeled CO2 show that the oxygen in O3 formed by the reaction of O2 with CO3 is in part derived from the CO2.

Interaction potentials and transport properties of coinage metal cations in rare gases

High-level ab initio calculations are performed on the coinage metal cations (Cu+, Ag+, and Au+) interacting with each of the rare gases [Rg (Rg=He to Rn)]. The RCCSD(T) procedure is employed, with basis sets being of approximately quintuple-zeta quality, but with the heavier species using relativistic effective core potentials. The interaction potentials are compared to experimental and theoretical data where they exist. In addition, transport coefficients for the mobility and diffusion of the cations in the rare gases are calculated. The latter have involved a rewriting of some of the programs used, and the required modifications are discussed. The mobility results indicate that, rather than being a rare occurrence, mobility minima may be common phenomena. Finally, a new estimate is put forward for the validity of zero-field mobilities in ion mobility spectrometry.

Spectroscopic characterization of the X(10+) and A(30+) states of CdNe, CdAr, CdKr, and CdXe

We report the spectroscopic characterization of the X(10+) and A(30+) states of CdNe, CdAr, CdKr, and CdXe. The van der Waals molecules were created in a free jet supersonic expansion and studied by low and high resolution laser‐induced fluorescence. CdAr was also studied by dispersed fluorescence. A method of analyzing rotationally structured vibrational bands of overlapping isotopic spectral contributions is discussed. Spectroscopic parameters are obtained from computer simulations of CdNe and CdAr spectra and from analysis of vibrational isotope splittings for CdKr and CdXe. CdNe: r‘e (X state)=4.26±0.05 A, re(A state) =3.62±0.05 A, D’e(A state) =77 cm−1; CdAr: r‘e(X) =4.33±0.04 A, r’e(A) =3.45±0.03 A, De(A) =325 cm−1; CdKr: D’e(A) =513 cm−1 and CdXe: De(A) =1086 cm−1.

Excitation spectra of CaAr, SrAr and BaAr molecules in a supersonic jet

Abstract Laser-induced excitation spectra of CaAr, SrAr, and BaAr produced in a supersonic jet apparatus were determined in the vicinity of the lowest 1 S 0 - 1 P 0 resonance lines of the free metal atoms. Spectroscopic constants of the X 1 Σ + and A 1 Π states of these molecules were determined and compared to those of the analogous MgAr states.

Ultraviolet Absorption Spectrum of Carbonyl Sulfide

The absorption coefficients of gaseous carbonyl sulfide have been measured in the spectral region 2000 to 2650 A. Band structure has been observed superimposed on apparently continuous absorption. The bands can be arranged into four progressions, one of which arises from population of an excited vibrational level of the ground electronic state. It is concluded from the temperature dependence of the long wavelength portion of the spectrum that the “continuous” absorption is due to a transition to a bent upper state of OCS, namely (1Δ)1A′ or (1Σ−)1A″.