David J. Funk

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.

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.

Half‐collision dynamics: Exclusive production of Cd(5s5p 3P2) from the predissociation of Cd(5s5p 1P1)⋅Xe electronic states

The CdXe(C 1Π1) state, correlating with Cd(5s5p 1P1)+Xe, undergoes efficient spin–orbit predissociation via the repulsive c 3∑1 state, producing Cd(5s5p 3P2)+Xe exclusively. This is consistent with the fact that the Cd(5s5p 1P1) atomic state is deactivated to Cd(5s5p 3P2 on nearly every collision with a Xe atom. The CdXe(D 1∑+0) state, excited above its dissociation limit, produces not only Cd(5s5p 1P1)+Xe but also a small yield of Cd(5s5p 3P2)+Xe. A mechanism is proposed in which the D 1∑+0 and C 1Π1 states are mixed via rotationally induced L uncoupling, leading to Cd(5s5p 3P2)+Xe by C 1Π1–c 3∑1 predissociation. This has implications related to the dynamical concept of ‘‘orbital following.’’ The dissociation energy D0 of the CdXe(X 1∑+0) ground state is also determined to be 176±5 cm−1.

A laser spectroscopic study of the X 1Σ+0−C 1Π1 transition of MgAr: Evidence for Λ‐type doubling

The X 1Σ+0 and the C 1Π1 states of MgAr have been characterized spectroscopically. The MgAr van der Waals molecules, created in a new laser‐vaporization, pulsed supersonic jet apparatus, were studied using laser‐induced fluorescence. High‐resolution spectra revealed lambda‐type doubling consistent with the presence of the nearby higher‐lying repulsive MgAr (D 1Σ+0) electronic state.

Half-collision studies of singlet-to-triplet energy transfer : action spectroscopy and predissociation dynamics of electronically excited Cd.H2 and Cd.D2 complexes

The Cd⋅H2 and Cd⋅D2 van der Waals complexes were synthesized by expanding cadmium vapor and He/H2 mixtures into a supersonic free jet. The ‘‘half‐collision’’ process, Cd(5s5p 1P1)⋅H2→Cd(5s5p 3PJ) +H2, was studied by fixing a probe dye laser pulse (delayed 10 ns) onto one of the Cd(5s6s 3S1←5s5p 3PJ) transitions while exciting the Cd⋅H2(Cd⋅D2) complex with a pump dye laser pulse tuned across frequencies near that of the free Cd(5s5p 1P1←5s5s 1S0) atomic transition. When the probe laser was tuned to detect Cd(5s5p 3P2), an action spectrum to the red of the atomic transition was obtained for Cd⋅H2 consisting of a broad continuum superimposed upon which was an anharmonic series of vibrational transitions with discernible, blue‐shaded rotational structure.A similar spectrum was recorded for Cd⋅D2, except that only very broadened blue‐shaded rotational structure was observed. From the isotopic band‐head splittings, computer simulations of the rotational band structure, and recent ab initio calculations of Cd⋅H2...

Mo/ller–Plesset perturbation theory calculation of alkaline earth–rare gas complexes: Ground states of Mg–He and Mg–Ar

We have used Mo/ller–Plesset perturbation theory as carried out through the fourth order for a determination of the potential parameters for the ground states of the alkaline–earth metal magnesium with argon and helium. Mg–He was found to have a potential minimum of ≈0.021 mhartree at an internuclear distance of 9.75 a0 and was determined to be capable of supporting a single vibrational level. Mg–Ar was found to have a potential minimum of ≈0.254 at an internuclear distance of 9 a0 , which is slightly shallower and at a larger internuclear distance than a recent experimental determination. A comparison of the homonuclear and heteronuclear bonding is presented and differences in the bonding are attributed to exchange–repulsion effects.

The interactions of metal atoms with Xe, CH4 and H2: half-collision studies

Abstract The interactions of ground-state and excited-state metal atoms with Xe, CH4, and H2 have been studied by the “half-collision” technique of action spectroscopy. Van der Waals complexes of ground-state Cd and Zn atoms with Xe, CH4, or H2 are synthesized at very low temperatures in a supersonic expansion. By tuning an excitation laser pulse to a frequency near that of an electronic transition of the free metal atom while monitoring the atomic state product of an energy transfer process with a second, delayed, laser pulse, it is often possible to obtain an “action” spectrum which yields information about the upper potential energy surface(s) on which the “full-collision” process occurs. Action spectra of singlet-to-triplet deactivations M(nsnp1P1)·Q → M(nsnp3PJ) + Q were determined for the Zn·Xe, Cd·Xe, Cd·CH4, and Cd·H2 complexes. For the Xe and CH4 cases, the spectra are consistent with a previously postulated collisional mechanism in which a repulsive “3Σ” state correlating with M(nsnp3P2) crosses an attractive “1Π” state correlating with M(nsnp1P1). For Cd·H2(Cd·D2) the spectra consist of a continuum, tentatively assigned as the predissociation of the strongly chemically bound 1B2 state, on which are superimposed progressions of vibrational transitions which are thought to be due to less efficient predissociation of the weakly bound, pseudo-diatomic 1B1 state. Action spectra of the intramultiplet deactivation Cd(5s5p3P1)·CH4 → Cd(5s5p3P0) + CH4 were also determined. From the simple pseudo-diatomic nature of the spectrum to the red of the atomic transition and successful simulations of the rotational structure of some of the bands as parallel transitions, it is postulated that the ground-state Cd·CH4 complex is the C3v hindered rotor nuclear-spin isomer E(K″ = 1), which is stabilized more by anisotropy than the lower-lying F(K″ = 0) and A(K″ = 0) isomers. The upper-state is therefore the E(K′ = 1) level of the “A3Π0+” electronic state of Cd·CH4.