A connection approach to the Einstein-Maxwell field equations

Scalar densities which are concomitants of the metric tensor, a symmetric affine connection and its first derivative, and the derivative of a vector field are examined. Rather simple demands are imposed on the corresponding Euler-Lagrange expressions. It is found that the associated field equations reduce essentially to the Einstein-Maxwell field equations.     

Stark spectroscopy with the CO laser: The ν3 fundamental band of H2CO

The ν₃ fundamental band of H₂CO (CH₂ scissoring motion) has been studied by means of CO laser Stark spectroscopy and conventional infrared absorption spectroscopy. The primary aim of the work was to determine the dipole moment of H₂CO in the v₃ = 1 state, and the value determined was 2.3250 ± 0.0025 D. The spectrum was analyzed with the inclusion of the Coriolis interactions among ν₃, ν₄, and ν₆ so that “true” rotational constants were determined for ν₃; “effective” constants obtained by ignoring these interactions were also determined. The ν₃ band origin was determined to be 1500.174 ± 0.002 cm^?1. The H₂CO spectrum was also used as a means of determining the frequencies of some ¹³C¹⁶O and ¹²C¹⁸O laser lines in the 1500 cm^?1 region relative to ¹²C¹⁶O lines.     

Infrared spectra of CO2-doped 4He clusters, 4HeN-CO2, with N=1-60

High resolution spectra of (4)He(N)-CO(2) clusters are studied in the region of the CO(2) nu(3) fundamental band (approximately 2300 cm(-1)). The clusters are produced in a pulsed supersonic jet expansion from a cooled nozzle source and probed by direct absorption using a tunable diode laser operating in a rapid-scan mode. Four carbon dioxide isotopes ((16)O(12)C(16)O, (16)O(13)C(16)O, (18)O(13)C(18)O, and (16)O(13)C(18)O) are used to support the analysis, and because additional rotational transitions are allowed for the asymmetric one ((16)O(13)C(18)O). Resolved R(0) (J=1<--0) rotation-vibration transitions are observed for clusters up to N=60. A detailed rotational analysis is possible up to N approximately 20 and, with some assumptions, to N approximately 37 and beyond. The derived rotational constants (B values) vary smoothly with N and show evidence for broad oscillations similar to those already reported for He(N)-OCS and He(N)-N(2)O. Possible indications of a disruption are observed in the J=2 levels of larger clusters (N>22) which could be caused by interactions with a "dark" helium cluster modes.     

Spectroscopic studies of OCS-doped 4He clusters with 9-72 helium atoms: observation of broad oscillations in the rotational moment of inertia

High-resolution spectra of HeN-OCS clusters with N up to 39 in the microwave region and up to 72 in the infrared region were observed with apparatus-limited line widths of about 15 kHz and 0.001 cm(-1), respectively. The cold (approximately 0.2 K) clusters were produced in pulsed supersonic jet expansions of very dilute OCS + He mixtures and probed using a microwave Fourier transform spectrometer or a tunable infrared diode laser spectrometer. Consistent analyses of the microwave and infrared data yield band origins for the carbonyl stretching vibration, together with rotational parameters for the ground and excited vibrational states. The rotational constant, B, passes through a minimum at N = 9 and then rises as the He atoms uncouple from the OCS rotational motion as a result of superfluid effects. There are broad unexpected oscillations in B, with maxima at N = 24 and 47 and minima at N = 36 and 62. The change in B upon vibrational excitation, which is negative for the OCS molecule, converges to positive values for N > 15. These results help to bridge the gap between individual molecules and bulk matter with atom-by-atom resolution over a significant range of cluster sizes.     

Observation of the "missing" polar OCS dimer

A new infrared band at 2069.3 cm-1 is observed and assigned to the long-anticipated polar isomer of the OCS dimer, helping to explain apparent discrepancies among earlier studies. The data reported here should enable direct observation of the microwave spectrum of polar (OCS)2 and motivate new theoretical works on the energetics of OCS dimer isomers and interconversion energy barriers.     

Line profile study of transitions in the 30012 ← 00001 and 30013 ← 00001 bands of carbon dioxide perturbed by air

In this work we present a line profile study for air-broadened carbon dioxide transitions in the 30012 ← 00001 and 30013 ← 00001 vibrational bands. The room temperature spectra were recorded at a resolution of 0.008 cm⁻¹ using a Fourier Transform spectrometer. The air-broadening, air-shift, and air-line mixing coefficients were derived from a simultaneous fitting of spectra using the Voigt model and a Speed-Dependent Voigt lineshape model. The results obtained are consistent with other studies in addition to the theoretically calculated values. Exponential Power Gap (EPG) and Energy Corrected Sudden (ECS) scaling laws were used to calculate the relaxation matrix elements.     

Infrared spectra of two isomers of OCS–C2H2 and OCS–C2D2 in the region of OCS ν1 fundamental

Infrared spectra of OCS–C₂H₂ and OCS–C₂D₂ complexes in the region of the C–O stretching fundamental of OCS (2060 cm⁻¹) are studied in a pulsed supersonic slit-jet expansion using a tunable diode laser. For each complex, two bands are observed and assigned to distinct near-parallel and the T-shaped isomers. Ground state parameters were previously determined from microwave studies, so analysis of the infrared spectra gives information on the vibrational shifts upon complex formation as well as rotational and centrifugal distortion parameters for the excited states. All four bands show a red shift with respect to the monomer band origin, with the T-shaped isomer having a much larger shift than the near-parallel isomer. Disappearance of the T-shaped isomer when argon is used as a carrier gas supports the notion that the near-parallel isomer is the lowest energy form of the complex.     

Infrared spectra of acetylene dimers and acetylene–nitrogen: (DCCD)2, H-bonded DCCD–HCCH, and DCCD–NN in the 4.1 μm region

Infrared spectra of the weakly-bound T-shaped acetylene dimers DCCD–DCCD and DCCD–HCCH are studied in the region of the DCCD ν₃ fundamental (∼2440 cm⁻¹) using a pulsed supersonic slit-jet expansion and a tunable diode laser probe. The K_a = 0 ← 1 and 1 ← 0 subbands, corresponding to the vibration of the DCCD monomer at the “top” of the T, are analyzed. Compared to the analogous spectrum of HCCH–HCCH, the present results are much less perturbed. The tunneling splitting for (DCCD)₂ in the excited state is determined to be 141 MHz, a big reduction from the previously determined ground state value of 424 MHz. The dimer A rotational constants show a large apparent increase upon vibrational excitation, and we discuss whether this increase is real. The linear DCCD–NN complex is also observed as an impurity in the spectrum, and it too is found to be unperturbed, in contrast with HCCH–NN.     

Millimeter-Wave Spectroscopy of Kr-CO and Xe-CO Using a Coaxial Jet Spectrometer

A new pulsed supersonic jet millimeter-wave spectrometer with coaxial propagation of the molecular jet and millimeter-waves has been constructed. The coaxial configuration provides greater sensitivity which has been demonstrated by observing b-type transitions of five isotopomers of Kr-(12)C(16)O and seven isotopomers of Xe-(12)C(16)O. These results were analyzed together with a-type transitions obtained by FTMW spectroscopy to determine improved rotational parameters for each isotopomer. The ground vibrational state K = 1 <-- 0 intervals have thus been precisely determined for Kr-CO and Xe-CO. Copyright 2001 Academic Press.