Search

We present limits on spin-independent dark matter-nucleon interactions using a $10.6$ $\mathrm{g}$ Si athermal phonon detector with a baseline energy resolution of $\sigma_E=3.86 \pm 0.04$ $(\mathrm{stat.})^{+0.19}_{-0.00}$ $(\mathrm{syst.})$ $\mathrm{eV}$. This exclusion analysis sets the most stringent dark matter-nucleon scattering cross-section limits achieved by a cryogenic detector for dark matter particle masses from $93$ to $140$ $\mathrm{MeV}/c^2$, with a raw exposure of $9.9$ $\mathrm{g}\cdot\mathrm{d}$ acquired at an above-ground facility. This work illustrates the scientific potential of detectors with athermal phonon sensors with eV-scale energy resolution for future dark matter searches., Comment: 7 pages, 4 figures, this version includes ancillary files from official data release

This corrects the article DOI: 10.1103/PhysRevLett.121.051301.

We present the first limits on inelastic electron-scattering dark matter and dark photon absorption using a prototype SuperCDMS detector having a charge resolution of 0.1 electron-hole pairs (CDMS HVeV, a 0.93 gram CDMS HV device). These electron-recoil limits significantly improve experimental constraints on dark matter particles with masses as low as 1 MeV/$\mathrm{c^2}$. We demonstrate a sensitivity to dark photons competitive with other leading approaches but using substantially less exposure (0.49 gram days). These results demonstrate the scientific potential of phonon-mediated semiconductor detectors that are sensitive to single electronic excitations., 6 pages + title and references, 6 figures, includes erratum submitted to PRL and data release

We report the result of a blinded search for weakly interacting massive particles (WIMPs) using the majority of the SuperCDMS Soudan data set. With an exposure of 1690 kg d, a single candidate event is observed, consistent with expected backgrounds. This analysis (combined with previous Ge results) sets an upper limit on the spin-independent WIMP–nucleon cross section of 1.4×10−44 (1.0×10−44) cm2 at 46 GeV/c2. These results set the strongest limits for WIMP–germanium-nucleus interactions for masses >12 GeV/c2.

Building on the successful experience in operating the DarkSide-50 detector, the DarkSide Collaboration is going to construct DarkSide-20k, a direct WIMP search detector using a two-phase Liquid Argon Time Projection Chamber (LAr TPC) with an active (fiducial) mass of 23 t (20 t). This paper describes a preliminary design for the experiment, in which the DarkSide-20k LAr TPC is deployed within a shield/veto with a spherical Liquid Scintillator Veto (LSV) inside a cylindrical Water Cherenkov Veto (WCV). This preliminary design provides a baseline for the experiment to achieve its physics goals, while further development work will lead to the final optimization of the detector parameters and an eventual technical design. Operation of DarkSide-50 demonstrated a major reduction in the dominant 39Ar background when using argon extracted from an underground source, before applying pulse shape analysis. Data from DarkSide-50, in combination with MC simulation and analytical modeling, shows that a rejection factor for discrimination between electron and nuclear recoils of $>3 \times 10^{9}$ is achievable. This, along with the use of the veto system and utilizing silicon photomultipliers in the LAr TPC, are the keys to unlocking the path to large LAr TPC detector masses, while maintaining an experiment in which less than $< 0.1$ events (other than $\nu$ -induced nuclear recoils) is expected to occur within the WIMP search region during the planned exposure. DarkSide-20k will have ultra-low backgrounds than can be measured in situ, giving sensitivity to WIMP-nucleon cross sections of $1.2 \times 10^{-47}$ cm2 ( $1.1 \times 10^{-46}$ cm2) for WIMPs of 1 TeV/c2 (10 TeV/c2) mass, to be achieved during a 5 yr run producing an exposure of 100 t yr free from any instrumental background.

© 2016 American Physical Society. The CDMS low ionization threshold experiment (CDMSlite) uses cryogenic germanium detectors operated at a relatively high bias voltage to amplify the phonon signal in the search for weakly interacting massive particles (WIMPs). Results are presented from the second CDMSlite run with an exposure of 70 kg day, which reached an energy threshold for electron recoils as low as 56 eV. A fiducialization cut reduces backgrounds below those previously reported by CDMSlite. New parameter space for the WIMP-nucleon spin-independent cross section is excluded for WIMP masses between 1.6 and 5.5 GeV/c2.

The lowest-lying isomers of the copper nonamer cluster, Cu 9 , are obtained from a genetic algorithm approach and density functional theory. Three isomers are found with relative energy differences of less than 0.07 eV, which makes the assignment of the global minimum structure difficult. The static electric dipole polarizabilities and dipole moments of these isomers are obtained from density functional theory employing a very extensive valence basis set together with an energy-consistent scalar relativistic pseudopotential for copper. The discrepancy between theoretically and experimentally obtained polarizabilities is discussed.

We report a first search for weakly interacting massive particles (WIMPs) using the background rejection capabilities of SuperCDMS. An exposure of 577 kg days was analyzed for WIMPs with mass

In a previous paper (G. Osmann et al. J. Mol. Spectrosc. 197, 262 (1999)) we calculated ab initio the potential-energy surfaces of the ground [Formula: see text]2A" and excited Ã2A' electronic states of the HO2 molecule; these two states correlate with a 2Π state at linearity and participate in a Renner effect interaction. In that paper, we also calculated the electric- and magnetic-dipole moment and transition-moment surfaces, and the spin-orbit coupling constant; we then simulated the à ® [Formula: see text] emission band system including both electric-dipole and magnetic-dipole transitions. We now calculate more points on the surfaces to cover a wider range of bending geometries, and then refine the surfaces by fitting to rovibronic term values for both electronic states simultaneously. In the fitting we include levels having J values up to 9/2 and term values up to about 8000 cm–1. In our calculation of the energy levels we allow for the Renner effect and spin-orbit coupling by using our variational computer program RENNER. A good fitting to the data is obtained and as a result we obtain an accurate representation of these two potential surfaces over an energy range of more than 1 eV. We tabulate the vibronic energies up to 1 eV for both HO2 and DO2. We can explain the origin of a perturbation observed in the F1 spin component levels of the Ã(0, 0, 0) vibronic state for J values around 51/2; this is caused by a spin-orbit interaction satisfying Δ N = ± 1 with the F2 spin component levels of the [Formula: see text](1,1,2) vibronic state. Using the new rovibronic energies and wave functions, with our ab initio electric dipole moment and transition moment surfaces, we calculate Stark coefficients and compare them with experiment for some ground vibronic state levels. PACS Nos.: 31.20D, 31.50, 33.10, 33.20E, 35.20D, 35.20J

We report results of a search for Weakly Interacting Massive Particles (WIMPS) with the silicon detectors of the CDMS II experiment. This blind analysis of 140.2 kg-days of data taken between July 2007 and September 2008 revealed three WIMP-candidate events with a surface-event background estimate of 0.41^{+0.20}_{-0.08}(stat.)^{+0.28}_{-0.24}(syst.). Other known backgrounds from neutrons and 206Pb are limited to < 0.13 and, 5 pages, 4 figures, as accepted by PRL

The ground X 2 A 1 electronic state of CH 2 + is quasilinear with a small barrier to linearity, and at linearity the state becomes degenerate with the A 2 B 1 electronic state forming a 2 Π u state. Because of the nonzero electronic angular momentum the rovibrational basis states belonging to the two electronic states strongly interact due to both the Renner effect and spin-orbit coupling. In a previous paper (P. Jensen, M. Brumm, W. P. Kraemer, and P. R. Bunker, J. Mol. Spectrosc. 172 (1995) 194) we calculated the rovibronic energies of the states using ab initio potential energy surfaces that we generated. In the present paper we use the electronic wavefunctions of the previous ab initio calculation to determine the dipole moment and transition moment surfaces, and we develop the theory that allows us to use these to calculate intensities. As a result we now calculate both the positions and intensities of the lines in the absorption spectrum of CH 2 + , and its deuterated isotopomers, making full allowance for the effects of the Renner interaction and of spin-orbit coupling. We predict the appearance of the absorption spectrum over the whole wavenumber range from 0 cm −1 to beyond 15 000 cm −1 ; this involves only the X and A electronic states. We hope that these results allow experimentalists to search successfully for the features that we predict, and thereby to achieve a better spectroscopic characterization of this important molecular ion.

SuperCDMS is an experiment designed to directly detect weakly interacting massive particles (WIMPs), a favored candidate for dark matter ubiquitous in the Universe. In this Letter, we present WIMP-search results using a calorimetric technique we call CDMSlite, which relies on voltage-assisted Luke-Neganov amplification of the ionization energy deposited by particle interactions. The data were collected with a single 0.6 kg germanium detector running for ten live days at the Soudan Underground Laboratory. A low energy threshold of 170 eVee (electron equivalent) was obtained, which allows us to constrain new WIMP-nucleon spin-independent parameter space for WIMP masses below 6 GeV/c2, Funding and support were received from the National Science Foundation, the Department of Energy, a Fermilab URA Visiting Scholar Award, NSERC Canada, and MULTIDARK. Fermilab is operated by the Fermi Research Alliance, LLC under Contract No. De-AC02- 07CH11359. SLAC is operated under Contract No. DEAC02- 76SF00515 with the United States Department of Energy

It has been established from earlier ab initio calculations that in its equilibrium configuration the CH+5 molecular ion consists of an H2 moiety bound to the apex of a pyramidal CH+3 group; the H2 group is approximately perpendicular to the C3 axis of the CH+3 group, and the binding energy is about 15000 cm−1. Two internal motions, the torsion and the flip, provide connections with low barriers between all 120 symmetrically equivalent minima on the potential energy surface so that all proton permutations are feasible. We present the results of new high level ab initio calculations of the parts of the potential energy surface associated with these two motions, and in particular we determine the continually optimized structure, and associated electronic energy, for the CH+5 molecular ion as it undergoes the flip motion. For the flip motion we numerically integrate the one‐dimensional Schrodinger equation for the tunneling to determine the splitting. Since this splitting is small (1.4 cm−1) we can incorpora...

Using millimeter wave absorption spectroscopy we have recorded pure rotation spectra of MgOH in its ground vibrational state and in six excited vibrational states. We have also determined a large number of bending vibrational energies, and the MgO stretching frequency, using dispersed fluorescence studies of both MgOH and MgOD. By a weighted least-squares optimized fitting to this data, using the vibrational approach MORBID (Morse oscillator rigid bender for internal dynamics), we have derived the full ground state potential surface in an analytical form. The equilibrium structure is determined to be linear but with a flat predominantly quartic bending potential.

In this paper we report the results of an ab initio calculation of vibronic (i.e., N = 0) energy levels of the CH2+ molecular ion giving the lowest 19 levels of the ground [Formula: see text] electronic state and the lowest 15 of the first excited Ã2B1 state. The two electronic states become degenerate (2Π) at the linear configuration and their rovibronic levels interact via the Renner effect. The ab initio calculation of the two potential surfaces was performed at 96 nuclear geometries for the ground electronic state, covering energies up to 11 000 cm−1 above equilibrium, and at 86 geometries for the excited state, covering energies up to 30 000 cm−1 above equilibrium. The multireference configuration interaction (MRCI) level of theory was used with molecular orbital bases that were optimized separately for each state by complete-active-space-self-consistent-field (CASSCF) calculations. The vibronic energy levels were calculated variationally from the potential surfaces using the Morse oscillator rigid bender internal dynamics Hamiltonian modified to include the effects of the Renner interaction. We also present calculated vibronic energies for the CD2+ and CHD+ isotopically substituted molecules.

We report results from a reanalysis of data from the Cryogenic Dark Matter Search (CDMS II) experiment at the Soudan Underground Laboratory. Data taken between October 2006 and September 2008 using eight germanium detectors are reanalyzed with a lowered, 2 keV recoil-energy threshold, to give increased sensitivity to interactions from Weakly Interacting Massive Particles (WIMPs) with masses below ~10 GeV/c^2. This analysis provides stronger constraints than previous CDMS II results for WIMP masses below 9 GeV/c^2 and excludes parameter space associated with possible low-mass WIMP signals from the DAMA/LIBRA and CoGeNT experiments., 9 pages, 8 figures. Supplemental material included as ancillary files. v3) Added appendix with additional details regarding energy scale and backgrounds

We report on the first axion search results from the Cryogenic Dark Matter Search (CDMS) experiment at the Soudan Underground Laboratory. An energy threshold of 2 keV for electron-recoil events allows a search for possible solar axion conversion into photons or local Galactic axion conversion into electrons in the germanium crystal detectors. The solar axion search sets an upper limit on the Primakov coupling $g_{a\gamma\gamma}$ of 2.4$ \times 10^{-9}$ GeV$^{-1}$ at the 95% confidence level for an axion mass less than 0.1 keV/c$^2$. This limit benefits from the first precise measurement of the absolute crystal plane orientations in this type of experiment. The Galactic axion search analysis sets a world-leading experimental upper limit on the axio-electric coupling $g_{a\bar{e}e}$ of 1.4$ \times 10^{-12}$ at the 90 % confidence level for an axion mass of 2.5 keV/c$^2$. This analysis excludes an interpretation of the DAMA annual modulation result in terms of Galactic axion interactions for axion masses above 1.4 keV/c$^2$., Comment: 5 pages, 5 figures

Calculations of far-infrared spectra for the weakly bound complexes (HF) 2 , (HCl) 2 and (HBr) 2 are reported. For (HF) 2 and (HCl) 2 , potentials fitted to ab initio data are used. Spectra are also predicted using simple classical potentials. The method involves diagonalising the Hamiltonian for the dimer with the monomer and intermolecular bond lengths held fixed. The approach gives very good agreement with energy levels calculated with the close coupling method, particularly for (HCl) 2 . Furthermore, the simple electrostatic potential gives a spectrum for (HCl) 2 that agrees surprisingly well with that obtained from the ab initio potential energy surface.

We have previously determined an analytical ab initio six-dimensional potential energy surface for the HCl dimer, and in the present paper we use this potential, with the HCl bond lengths held fixed, in a full (four-dimensional) close-coupling calculation to determine the energies of the lowest 24 vibrational states. These vibrational states involve the intermolecular stretch ν 4 , the trans-bend tunneling vibration ν 5 , and the torsion ν 6 . The highest of the 24 levels is the (ν 4 ν 5 ν 6 )=(111) state, for which we calculate an energy of 200 cm −1 above the (000) state. As well as determining tunneling energies up to 5ν 5 =183 cm −1 , we determine ν 4 =49 cm −1 , 2ν 4 =93 cm −1 , 3ν 4 =134 cm −1 , 4ν 4 =172 cm −1 , ν 6 =137 cm −1 and ν 4 +ν 6 =178 cm −1 , together with tunneling energies in all these states. Making allowance for the HCl stretching zero-point energy we determine the dissociation energy D 0 as 390 cm −1 on this analytical surface. We determine that below 300 cm −1 there are 72 vibrational ( J=K =0) states, and below dissociation there are 162 vibrational ( J=K =0) states, for this potential surface.

The potential energy surface of the hydrogen chloride dimer has been investigated within the framework of the averaged coupled pair functional (ACPF) approach applying two extended, polarized basis sets. With the larger basis set which includes f functions, 606 individual points have been computed, mainly for planar configurations, whereas with the smaller basis set 1654 points, among them a substantial number of non-planar geometries, have been evaluated on the 6D energy surface. The characteristic features of the potential energy surface are discussed with the aid of a series of contour plots for various selected 2D cuts through the energy surface, and a detailed comparison to the related case of the hydrogen fluoride dimer is given. Several stationary points have been located and optimized structural parameters for these are reported. For the more important ones, those that determine the shape of the minimum energy path of the spectroscopically observable trans-bending tunneling motion, harmonic vibrational frequencies are reported as well. This minimum energy path differs qualitatively from that in the hydrogen fluoride dimer.

We report results from the Cryogenic Dark Matter Search at the Soudan Underground Laboratory (CDMS II) featuring the full complement of 30 detectors. A blind analysis of data taken between October 2006 and July 2007 sets an upper limit on the weakly interacting massive particle (WIMP) nucleon spin-independent cross section of 6.6x10;{-44} cm;{2} (4.6x10;{-44} cm;{2} when combined with previous CDMS II data) at the 90% confidence level for a WIMP mass of 60 GeV/c;{2}. This achieves the best sensitivity for dark matter WIMPs with masses above 44 GeV/c;{2}, and significantly restricts the parameter space for some favored supersymmetric models.

We have carried out an ab initio calculation of the intramolecular stretching spectra (wave numbers and transition moments) of (HF)2, (DF)2, and HFDF involving v1+v2≤3, where v1 and v2 are the local mode quantum numbers for the two intramolecular (HF or DF) stretches. The ab initio surface used as a basis for these calculations has already been published [M. Kofranek, H. Lischka, and A. Karpfen, Chem. Phys. 121, 137 (1988); P. R. Bunker, P. Jensen, A. Karpfen, M. Kofranek, and H. Lischka, J. Chem. Phys. 92, 7432 (1990)], but in the present work we have extended the 1520 nuclear geometry points previously available with 198 points in order to explore further the variation of the intramolecular stretching energies and the dipole moment along the minimum energy (trans tunneling) path. We compute the intramolecular stretching energies and transition moments by making an adiabatic separation of the intramolecular stretching motion and the other vibrational motions of the molecules, and we use the semirigid ben...

For the HF dimer we calculate the fundamental HF stretching vibration frequencies, and the fundamental and overtone frequencies of the intermolecular (HF–HF) stretching vibration, using an ab initio potential energy surface and the previously developed semirigid bender Hamiltonian. The ab initio surface used involves the addition of 459 nuclear geometry points to the 1061 reported in our earlier work. These extra points have been chosen to give more information on those parts of the surface that involve distortions of the HF bond lengths. We have fitted these 1520 points to an analytic expression, slightly modified from our previous work, that involves 39 adjustable parameters and one constrained parameter; the weighted standard deviation of the fit is 29.3 cm−1. To calculate the vibrational frequencies, and the tunneling splittings in these vibrationally excited states, we use the semirigid bender Hamiltonian to average over the trans‐tunneling path. We also calculate from the ab initio surface the effec...

The occurrence of internal-rotation-like motion of the three protons around the CC core in C2H3+ was discovered by ab initio calculation some time ago, and using an ab initio potential we have previously calculated the splittings of the rotational levels that result from the tunneling between the six identical minima in the potential. Recently the splittings in a CH stretching fundamental band have been measured by Crofton, Tagod, Rehfuss and Oka. In the present paper we attempt to determine an effective tunneling potential in the excited CH stretching state by fitting to the observed splittings. We discuss possible perturbations to the splittings that appear to spoil any attempt at a simple analysis.

We report new results from the Cryogenic Dark Matter Search (CDMS II) at the Soudan Underground Laboratory. Two towers, each consisting of six detectors, were operated for 74.5 live days, giving spectrum-weighted exposures of 34 kg-d for germanium and 12 kg-d for silicon targets after cuts, averaged over recoil energies 10-100 keV for a WIMP mass of 60GeV/c{sup 2}. A blind analysis was conducted, incorporating improved techniques for rejecting surface events. No WIMP signal exceeding expected backgrounds was observed. When combined with our previous results from Soudan, the 90% C.L. upper limit on the spin-independent WIMP-nucleon cross section is 1.6 x 10{sup -43} cm{sup 2} from Ge, and 3 x 10{sup -42} cm{sup 2} from Si, for a WIMP mass of 60GeV/c{sup 2}. The combined limit from Ge (Si) is a factor of 2.5 (10) lower than our previous results, and constrains predictions of supersymmetric models.

We report the first results from a search for weakly interacting massive particles (WIMPs) in the Cryogenic Dark Matter Search (CDMS) experiment at the Soudan Underground Laboratory. Four Ge and two Si detectors were operated for 52.6 live days, providing 19.4 kg-d of Ge net exposure after cuts for recoil energies between 10--100 keV. A blind analysis was performed using only calibration data to define the energy threshold and selection criteria for nuclear-recoil candidates. Using the standard dark-matter halo and nuclear-physics WIMP model, these data set the world's lowest exclusion limits on the coherent WIMP-nucleon scalar cross-section for all WIMP masses above 15 GeV, ruling out a significant range of neutralino supersymmetric models. The minimum of this limit curve at the 90% C.L. is 4 x 10^{-43} cm^2 at a WIMP mass of 60 GeV., Comment: 4 pages, 5 figures, submitted to Phys. Rev. Lett; minor clarifications in response to referee's comments

Using the example of the HCN molecule, we study theoretically the possibility of selectively breaking the stronger bond in a triatomic molecule by rotationally accelerating it in an optical centrifuge using a combination of two oppositely chirped and counter-rotating strong laser fields. In our simulation the resultant field forces rotational acceleration of the HCN molecule to a point where the centrifugal force between the two heavy atoms (C and N) exceeds the strength of their (triple) bond. The effects of bending, rovibrational coupling, and the Coriolis force, which conspire to prevent the molecule from rotational dissociation into HC + N, can be efficiently counteracted by simple optimization of the frequency chirp.

The Cryogenic Dark Matter Search (CDMS) employs low-temperature Ge and Si detectors to search for Weakly Interacting Massive Particles (WIMPs) via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. For recoil energies above 10 keV, events due to background photons are rejected with >99.9% efficiency, and surface events are rejected with >95% efficiency. The estimate of the background due to neutrons is based primarily on the observation of multiple-scatter events that should all be neutrons. Data selection is determined primarily by examining calibration data and vetoed events. Resulting efficiencies should be accurate to about 10%. Results of CDMS data from 1998 and 1999 with a relaxed fiducial-volume cut (resulting in 15.8 kg-days exposure on Ge) are consistent with an earlier analysis with a more restrictive fiducial-volume cut. Twenty-three WIMP candidate events are observed, but these events are consistent with a background from neutrons in all ways tested. Resulting limits on the spin-independent WIMP-nucleon elastic-scattering cross-section exclude unexplored parameter space for WIMPs with masses between 10-70 GeV c^{-2}. These limits border, but do not exclude, parameter space allowed by supersymmetry models and accelerator constraints. Results are compatible with some regions reported as allowed at 3-sigma by the annual-modulation measurement of the DAMA collaboration. However, under the assumptions of standard WIMP interactions and a standard halo, the results are incompatible with the DAMA most likely value at >99.9% CL, and are incompatible with the model-independent annual-modulation signal of DAMA at 99.99% CL in the asymptotic limit., 40 pages, 49 figures (4 in color), submitted to Phys. Rev. D; v.2:clarified conclusions, added content and references based on referee's and readers' comments; v.3: clarified introductory sections, added figure based on referee's comments

In this work, the XB12 and AA12 electronic states of the phosphino (PH2) free radical have been studied by dispersed fluorescence and ab initio methods. PH2 molecules were produced in a molecular free-jet apparatus by laser vaporizing a silicon rod in the presence of phosphine (PH3) gas diluted in helium. The laser-induced fluorescence, from the excited AA12 electronic state down to the ground electronic state, was dispersed and analyzed. Ten (υ1υ2υ3) vibrationally excited levels of the ground electronic state, with υ1⩽2, υ2⩽6, and υ3=0, have been observed. Ab initio potential-energy surfaces for the XB12 and AA12 electronic states have been calculated at 210 points. These two states correlate with a Πu2 state at linearity and they interact by the Renner-Teller coupling and spin-orbit coupling. Using the ab initio potential-energy surfaces with our RENNER computer program system, the vibronic structure and relative intensities of the AA12→XB12 emission band system have been calculated in order to c...

The B1A1 electronic state of silylene (SiH2) is the second excited singlet state of the molecule and, like the analogous c state of methylene (CH2), it is quasilinear with symmetry 1sigmag+ at linearity. This state dissociates to Si(1D) + H2(1sigmag+). At equilibrium, the B state of SiH2 has an energy that we calculate to be 0.71 eV above that of the dissociation products. However, there is a barrier to dissociation that allows quasibound rovibrational levels to occur, and some have been observed recently [Y. Muramoto et al., J. Chem. Phys. 122, 154302 (2005)]. Starting with our analytical ab initio potential-energy surface, we adjusted it in a fitting to the experimental term values in order to determine the optimum potential-energy function in the bound region. This potential has a C2v equilibrium structure with a SiH bond length of 1.459 angstroms and a bond angle of 165.4 degrees; the barrier to linearity is only 129 cm(-1). Using the optimized potential-energy surface we calculate B-state term values, and using our calculated y and z dipole moment surfaces, we simulate the rotation-vibration spectrum of the state in order to assist in the detection of the matrix isolation spectrum.

Thirty-five points on the potential energy surface of the ā3B1 first excited state for the GeH2 radical have been calculated using the (ab initio) MRD CI technique. Thirteen parameters in an analytic expression for the potential have been adjusted (by least-squares optimization) so that the surface fits these points. The rotation-vibration energy levels of GeH2. GeD2 and GeHD have been calculated using the non-rigid bender Hamiltonian, and we determine for GeH2 that ν1 = 1991 cm-1. ν2 = 763 cm-1, and ν3 = 2012 cm-1. The equilibrium structure is found to be re = 1.545 A and αz = 119.8°, and the singlet-triplet splitting is calculated to be 22.8 kcal/mole (7975 cm-1).

Fifty-four points on the potential energy surface of the ground electronic state of the ammonia molecule, with energies up to 9700 cm–1 above equilibrium, have been calculated ab initio using the configuration interaction technique. An analytic potential function has been fitted through these points and the rotation–vibration energy levels have been calculated using the nonrigid invertor Hamiltonian. The agreement with experiment is satisfactory enough that the anharmonic force constants obtained can be realistically used to assist in the interpretation of anharmonicity effects in the spectrum. We calculate the equilibrium bond length as 1.016 Å, the equilibrium HNH angle as 106.2°, and the invertion barrier as 1995 cm−1.

Using a purely ab initio minimum energy path for the trans‐tunneling motion in the HF dimer, the energy levels for the K‐type rotation and trans‐tunneling motion for (HF)2 and (DF)2 are calculated with a one‐dimensional semirigid bender Hamiltonian and no adjustable parameters. The transition moments for rotation‐tunneling transitions are calculated, using our ab initio value for the dipole moment of an isolated HF molecule, and we also calculate B values. The energy levels we obtain are in close agreement with experiment; for example, the K=0 tunneling splitting in (HF)2 is calculated as 0.65 cm−1 compared to the experimental value of 0.658 69 cm−1. As well as showing that our ab initio minimum energy path is very good, the calculation demonstrates that the semirigid bender formalism is able to account quantitatively for the unusual Kdependence of the rotational energies resulting from the quasilinear behavior, and that the trans‐tunneling motion is separable from the other degrees of freedom. We use th...

We have developed a semirigid bender model Hamiltonian to calculate the rotation and internal-rotation energy levels of ArH3+ and ArD3+. We have used this Hamiltonian to fit the data reported in M. Bogey, H. Bolvin, C. Demuynck and J.L. Destombes, Phys. Rev. Letters 58 (1987) 988. From the results of the fitting we can predict other rotation and internal l-rotation states that are amenable to experimental study. We predict that the torsional fundamental band of ArH3+, and the Ar-H3+ stretching fundamental band, will be in the 450–550 cm−1 region; these bands will interact as a result of c-type Coriolis coupling.

We simulate the photoelectron spectrum of CH−2 using the known bending potential functions of CH2 in the X 3B1 and a 1A1 states, together with a bending potential function and temperature for CH−2 in the X 2B1 state that are adjusted in order to fit the experimental spectrum. We find that in order to reproduce the spectrum we must have a CH−2 temperature of about 2500 K and a singlet–triplet separation in CH2 of 3250±200 cm−1 (0.40±0.02 eV or 9.3±0.6 kcal/mol). This leads to a value for the electron affinity of X state CH2 of 0.65±0.02 eV. In the simulation we include rotational levels with J (or N) up to 20, which means that over 500 000 rovibronic transitions are involved.

For the X 3B1, a1A1 and b 1B1 electronic states of the NH2+ molecular ion we have calculated ab initio points on the potential energy surfaces using a complete second-order configuration interaction calculation for the six valence electrons. For the X and a states the rotation-vibration energies were calculated from these surfaces using the MORBID Hamiltonian. For the X state we obtain re = 1.0338 A, αe = 153.17°, and a barrier to linearity of only 209 cm−1. Our best estimate for the vibrational frequencies are ν1 = 3118 cm−1, ν2 = 918 cm−1 and ν3 = 3363 cm−1. For the a state we obtain re = 1.0510 A, αe = 108.37°, ν1 = 3027 cm−1, ν2 = 1289 cm−1, and ν3 = 3111 cm−1.

We have simulated the photoelectron spectrum of CH−2 using the model described previously [Sears and Bunker, J. Chem. Phys. 79, 5265 (1983)]. The optimization of the fit of the simulated spectrum to the recently observed spectrum of Lineberger and co‐workers [J. Chem. Phys. 81, 1048 (1984) and preceding paper] has enabled us to determine the rotation‐bending energy levels of triplet CH2 over an energy range of more than 1 eV. It has also enabled us to determine that the rotational temperature of the CH−2 in the experiment is 220 K and that, for v2=1, the vibrational temperature is 680 K. For CH−2 we determine that ae=103° and that ν2=1230 cm−1. The singlet–triplet splitting in methylene is determined to be 3150±30 cm−1 (0.3905±0.004 eV, 9.01±0.09 kcal/mol) from the photoelectron spectrum, in excellent agreement with the more accurate value previously obtained from LMR spectroscopy [McKellar et al., J. Chem. Phys. 79, 5251 (1983)] of 3165±20 cm−1 (0.3924±0.0025 eV, 9.05±0.06 kcal/mol), and the electron aff...

We have developed an analytical expression for the 6D potential energy surface of (HF)2 and fitted it to 1061 ab initio points covering an energy range of up to 25 000 cm−1 above equilibrium. The ab initio calculation used the coupled pair functional approach with an extended polarized basis set. We have adjusted 42 parameters (and constrained 7 others) in the fitting of the analytical function to the points; the standard deviation of the weighted fitting is 26.8 cm−1 . The minimum energy path from the linear saddle point (345 cm−1 above equilibrium), through the equilibrium point, to the C2h saddle point (332 cm−1 above equilibrium) has been determined, and several cuts through the potential are presented. We plan to use this potential surface in reaction path and close coupling calculations of rotation–vibration term values.

In this paper we use the nonrigid bender Hamiltonian to calculate the rotation–vibration energy levels of 12CH2, 12CD2, and 13CH2 in the X 3B1 ground state. We adjust the shape of the potential surface used in the calculation in order to optimize the fit of the calculated energy level separations to the 61 available experimental values for these three isotopes of methylene. In the fit we vary nine parameters and determine, among other things, that the equilibrium bond length is 1.0748±0.0004 A, the equilibrium bond angle is 133.84°±0.05°, the height of the barrier to linearity is 1940±80 cm−1, and the optimum bond length for the molecule when it is linear, at the saddle point in the potential surface, is 1.060±0.005 A. From our results we predict the stretching frequencies in 12CH2 to be ν1=2950±40 cm−1 and ν3=3080±40 cm−1.

The Morse oscillator‐rigid bender internal dynamics (MORBID) Hamiltonian [P. Jensen, J. Mol. Spectrosc. 128, 478 (1988)] has been used in a fitting to all extant rotation–vibration data for X 3B1 methylene CH2. This fitting leads to an improved determination of the potential energy surface, and in particular to reliable predictions for the stretching frequencies. We predict ν1=2992 cm−1 and ν3=3213 cm−1 for 12CH2, and we hope that the new predictions will encourage the experimental search for these weak fundamentals. In the MORBID approach the rotation–vibration energies are obtained from the potential energy surface in a purely variational calculation, and consequently the present work is an improvement over previous determinations of the CH2 potential energy surface from experiment that used the nonrigid bender formalism [see P. R. Bunker et al., J. Chem. Phys. 85, 3724 (1986), and references therein]; this latter approach treats the stretching vibrations by second order perturbation theory. A fitting ...

The data in the two immediately preceding papers, when combined with the extant microwave, infrared, and photodetachment spectroscopic data, provide 152 rotation and rotation‐bending energy level separations in X 3B1 methylene (involving 12CH2, 13CH2, and CD2). In the present paper we fit all this data using the two nonrigid bender Hamiltonians NRB1 and NRB2. The more refined model (NRB2) leads to the following results for triplet methylene: re=1.0766±0.0014 A, αe=134.037°±0.045°, and the barrier height to linearity=1931±30 cm−1 (the uncertainties are three times the standard errors). Rotation‐bending energy levels for CH2, CD2, and CHD are calculated for v2≤4 and N≤6. The determination of the rotation‐bending energy levels in CH2 leads to an improved determination of the singlet–triplet splitting T0(a1A1) in methylene as 3156±5 cm−1 (9.023±0.014 kcal/mol, 0.3913±0.0006 eV). Although the rotation‐bending energy levels are accurately predicted it is not possible to predict the stretching frequencies of C...

The molecular symmetry group of the Van der Waals complex (H2)2 or (D2)2 is a group of order 16 called G16. This group is used to symmetry label the rotation–vibration states and the nuclear spin states of the complexes; the nuclear spin statistical weights are also determined. The group is used to classify the terms in the expansion of the dipole moment function and to determine the symmetry restrictions for allowed electric dipole transitions. The complex H2–D2 has a molecular symmetry group of order 8, G8, and (HD)2 a group of order 4, G4; the energy level symmetries, statistical weights, and selection rules for these complexes are also determined.

By fitting the eigenvalues of the nonrigid bender Hamiltonian to the 26 available experimental rotation‐vibration energy level splittings of the 3B1 ground electronic state of the methylene radical CH2 we determine the equilibrium geometry and potential function; the data only involve rotational transitions and transitions in the ν2 bending fundamental band. From the fit we determine that the equilibrium bond length is 1.075 A, the equilibrium bond angle is 133.9° and the height of the barrier to linearity is 1878 cm−1. We are able to use the nonrigid bender Hamiltonian, with this potential, to predict all the lower rotation‐vibration energy levels, including the ν1 and ν3 band origins, of CH2 and its isotopes.

Ten rotation–vibration transitions in the ν2 (bending) fundamental band of CH2 in its 3B1 ground electronic state have been measured and assigned using the technique of intracavity CO2 laser magnetic resonance (LMR) spectroscopy in the region 880–1090 cm−1. Using the present data, and the microwave and far‐infrared LMR measurements of pure rotational transitions, an effective bending potential energy curve has been derived for CH2 using the semirigid bender Hamiltonian. The bending frequency of CH2 is determined to be ν2=963.0987(4) cm−1, which is considerably lower than previous theoretical and experimental estimates.

High resolution measurements of the two components of the ν2 (umbrella) fundamental mode of the fully deuterated oxonium ion (D3O+) are reported. The spectra were obtained by diode laser absorption in a plasma containing D2 and D2O. Analysis of the observed spectra yields precise estimates of the two band origins and molecular parameters describing the states involved. By combining these data with the available high resolution data for H3O+, using the nonrigid invertor Hamiltonian, we are able to determine the equilibrium structure and the vibrational potential function; also we predict the inversion spectrum of D3O+ and the 2v2–v2 hot band spectra of H3O+ and D3O+.

Within the Born-Oppenheimer approximation homopolar isotopically unsymmetric diatomic ions (HD+, 14N15N+, 35Cl37Cl+, etc.) have D∞h symmetry and a non-vanishing dipole moment. This apparent paradox is reconciled here by treating carefully the transformation properties of the dipole moment operator in the D∞h group.

We have calculated 64 points on the ground electronic state potential energy surface of the silyl radical (SiH 3 ) using the MRD CI technique. This potential surface gives an inversion barrier of 1951 cm −1 and an equilibrium geometry of r e = 1.480 A and α e (HSiH) = 111.2°. Using the non-rigid invertor Hamiltonian with this potential we determine for SiH 3 that ν 1 = 2424 cm −1 , ν 2 = 778 cm −1 , ν 3 = 2106 cm −1 , and ν 4 = 976 cm −1 ; the inversion splitting is calculated to be 0.11 cm −1 . Rotational constants and centrifugal distortion constants have also been calculated.

Thirteen pure rotational transitions of CH2 in its X 3B1 ground vibronic state have been measured and assigned using the technique of far‐infrared laser magnetic resonance (LMR) spectroscopy. The energy levels thus determined led to the prediction and subsequent detection by microwave spectroscopy of a further rotational transition 404–313, at lower frequency (∼70 GHz). The analysis of these observations yields precise rotational constants as well as spin–spin, spin‐rotation, and hyperfine interaction parameters for gas phase CH2. Its rotational spectrum may enable interstellar CH2 to be detected by radio astronomy. Two rotaional transitions within the v1=1 excited vibrational state have also been identified in the LMR spectrum. Future observations of vibrationally excited CH2 may afford a means of determining the singlet–triplet splitting in methylene, and studies of CD2 and CHD will result in improved structural determinations.