Spin Doubling Research Articles

A laboratory and theoretical study of silicon hydroxide SiOH

The rotational spectrum of the triatomic free radical SiOH in its X (2)A(') ground electronic state has been observed in a supersonic molecular beam by Fourier transform microwave spectroscopy. The fundamental (1(0,1)-->0(0,0)) transition has been detected for normal SiOH and for three rare isotopic species: (30)SiOH, Si(18)OH, and SiOD. The same transition has also been observed in two of three excited vibrational states, v(2) and v(3), for the most abundant species. Precise spectroscopic constants, including those that describe the effective spin doubling and hydrogen hyperfine structure, have been derived for each isotopic species or vibrational state. To complement the laboratory work, theoretical calculations of the structure, dipole moment, and energies of the X (2)A(') and low-lying 1 (2)A(") states have also been undertaken at the coupled cluster level of theory. In agreement with theoretical predictions, we conclude from the hyperfine constants that SiOH is a best described as a pi-type radical, with the unpaired electron localized on a p orbital on the silicon atom. Assuming a bond angle of 118.5 degrees , the Si-O bond length is 1.647(2) A and the O-H bond length is 0.969(4) A.

Rotational Spectrum and Hydrogen Bonding of the H2O−HO Radical Complex

The first spectroscopic identification of the H2O-HO radical complex in the gas phase has been conducted by utilizing pulsed-discharge nozzle Fourier transform microwave spectroscopy. R-branch transitions in the Ka = 0 manifold appeared as in Hund's case (b), but extraordinarily large spin doubling implies a strong spin-orbit coupling between the electronic ground and low-lying excited states that correlate to the degenerate 2Pi state in free OH. The geometry of the complex is of C2v symmetry as a zero-point vibrational average, in which the OH radical acts as a proton donor to water. Precisely determined hyperfine coupling constants associated with hydrogen nuclei indicate a substantial rearrangement in unpaired electron distribution: there exists small but nonzero spin density on the H atoms in water.

The Radio Spectrum of the Phenyl Radical

The phenyl radical, C6H5, derived from benzene by removal of one hydrogen atom, was detected at centimeter wavelengths in a pulsed supersonic molecular beam and subsequently at millimeter wavelengths in a low-pressure direct current glow discharge. Fourteen rotational transitions between 9 and 40 GHz and over 50 transitions between 150 and 330 GHz, each split by spin doubling, have been measured for the normal isotopic species, and a comparable number have been measured for the fully deuterated species. The spectrum of both isotopic species at millimeter wavelengths is reproduced to an uncertainty of 0.5 km s-1 or better with seven spectroscopic constants. Rotational constants predicted from high-level molecular structure calculations are in excellent agreement with the measurements. Phenyl is a prime candidate for astronomical detection, because it is the prototypical aromatic hydrocarbon radical and a possible progenitor of other aromatic species.

Optical–optical double resonance of NO2 in the region of 612–614 nm: The role of 2A1 vibronic levels as dark and perturbing state

An optical–optical double resonance (OODR) technique has been applied to the rotational analysis and vibronic assignment of NO2 absorption band in the region of 612–614 nm. The two step excitation through 2 2B2←2B2←X̃ 2A1 has allowed us to determine rotational quantum numbers (NKa,Kc) for 73 eigenstates with B2 vibronic symmetry, lying at 16 306–16 465 cm−1 above the ground state. Although they are severely perturbed and irregular in the rotational structure and spin doubling, we can classify the rovibronic levels as four stacks; two Ka=0 stacks with subband origins of 16 306.2 and 16 321.0 cm−1, and two Ka=1 stacks with origins of 16 312.5 and 16 326.0 cm−1. A near-prolate asymmetric top approximation is used to obtain the term values and rotational constants. Extraordinary large DN measured for 2B2 vibronic levels can be understood by well-known, strong vibronic coupling between à 2B2 and highly excited vibrational levels of X̃ 2A1. Among a number of perturbations observed, the spin–orbit (and/or orbital–rotation) coupling between ‘‘light’’ 2B2 and ‘‘dark’’ 2A1 vibronic levels is clearly shown for the first time by analyzing intensity patterns of the ν2 -scanned (second step) OODR spectra.

Laser-induced fluorescence in the B̃–X̃ system of the HCO radical

The spectroscopy of the B̃ 2A′–X̃ 2A′ system of the formyl radical has been studied by laser-induced fluorescence. HCO was generated by photolysis of acetaldehyde, and a tunable laser operated near 245 nm excited eight bands of B̃–X̃. The (0,0,2)–(0,0,0) band has been rotationally analyzed, yielding A′=14.46 cm−1 and (B′+C′)/2=1.13 cm−1 for this slightly asymmetric top; asymmetry splitting and spin doubling are observed. The intense branches have ΔK=0 but there also are weaker perpendicular components with the transition moment near the b axis. Vibronic transition energies agree with those from matrix absorption but with a 130 cm−1 blueshift. Resolved fluorescence spectra to X̃ levels as high as 15 000 cm−1 furnish vibrational constants for the ground state.

The B 2Σ+-X 2Σ+ system of AlO

Eighteen bands of the Delta v=+4, +3 and -2 sequences of the B 2 Sigma +-X 2 Sigma + system of AlO have been photographed at high resolution and analysed for the rotational structure. It has been found that the spin-doubling constant gamma in the X 2 Sigma + state increases very rapidly with the vibrational quantum number v, while in the B state it remains almost constant and does not change with v. Also, the spin doubling in the v"=4, 5, 6 and 7 levels of the X 2 Sigma + state is not simply a linear function of N as found by earlier workers. It is found necessary to include a cubic term in N in the formula for the observed spin doubling in the X 2 Sigma + state. The unusual increase in the spin doubling is attributed to the proximity and the interactions of the vibrational levels of the A 2 Pi i state with the vibrational levels of the X 2 Sigma + state.

Rotational and translational cooling of molecular ions produced in a slot nozzle

Excimer laser drilling has been used to cut a 20-μm by 5-mm slot in the end of a closed Pyrex tube. The slot nozzle thus formed is suitable for production of a corona-excited supersonic expansion. The performance of the device has been characterized by recording the spectrum of the N+2B–X(0, 0) band at high resolution with the optical axis parallel to the slot and with the axis perpendicular to the slot (simulating a standard pinhole nozzle expansion) for comparison. The spectral lines recorded parallel to the slot nozzle are found to have a Doppler width such that a spin doubling of 0.06 cm−1 is resolved, while the pinhole-type spectrum resolves spin doubling of 0.09 cm−1. The slot nozzle also enhances the intensity of the spectrum, reducing recording time from 10 to 2 min, while maintaining the same approximate rotational temperature of 20–40% K.

Laboratory detection of the C3N an C4H free radicals

The millimeter-wave spectra of the linear carbon chain free radicals C3N and C4H, first identified in IRC + 10216 and hitherto observed only in a few astronomical sources, have been detected with a Zeeman-modulated spectrometer in laboratory glow discharges through low pressure flowing mixtures of N2 + HC3N and He + HCCH, respectively. Four successive rotational transitions between 168 and 198 GHz have been measured for C3N, and five rotational transitions between 143 and 200 GHz for C4H; each is a well-resolved spin doublet owing to the unpaired electron present in both species. Precise values for the rotational, centrifugal distortion, and spin doubling constants have been obtained, which, with hyperfine constants derived from observations of the lower rotational transitions in the astronomical source TMC 1, allow all the rotational transitions of C3N and C4H at frequencies less than 300 GHz to be calculated to an absolute accuracy exceeding 1 ppm.

New analysis of the (0,0) band of the 2Π → 2Σ transition of TiN

From new spectra and by the use of a better computation procedure it has been possible to improve the rotational analysis of the (0,0) band of the red system of TiN. In particular, the spin doubling of the lower 2Σ state has been resolved and two new perturbations have been identified in the 2Π state. The inclusion of high values of J yields more accurate molecular constants.

Interferometric measurements of linewidths and spin doubling in the N_2^+ first negative band system in free-jet expansions

The lower rotational R and P branch lines of the N2+ first negative band, 0–0 vibrational transition, have been studied interferometrically. Spectral source temperatures less than 20 °K were obtained using a free-jet expansion. The first negative system was produced with a beam of 30 keV electrons and the spin doubling and spectral line shape of a given rotational line was observed with a Fabry–Perot interferometer. It was found that the values of the spin-doubling constants, as determined independently from R and P branch measurements, were not consistent, i.e., different values were obtained from the R and P branch data. This implies that the interpretation of the doublet splittings as spin doubling is incomplete. Furthermore, it was found that the measured linewidths indicated temperatures of about 70 °K greater than the actual gas temperature. These discrepancies are attributed to hyperfine structure.

Spin doubling in CaH

The computation of Λ-doublet splittings in diatomic 2Π electronic states has become almost routine with accuracies of 1% obtainable for light hydrides. The spin−doubling which occurs in 2Σ states has received less attention: the only example seriously studied is HF+. Here this work is extended to CaH. Apart from the effects introduced by incorporating a third-row atom, CaH is of intrinsic value as its spectrum is of importance in resolving the puzzle of the apparent depletion of Ca in the interstellar medium relative to its abundance in stars.

Rotational analysis of the ultraviolet bands of PS

The 2-0, 1-0 and 0-0 bands of the ultraviolet system of PS have been analysed for their rotational structure. It is shown that they involve the transitionC2Σ -X2 Πr(a). TheC2Σ state shows a significant spin doubling.

G-tensor and spin doubling constant in the 2Σ molecules CN and C 2H

Free-molecule perpendicular g factor shifts (Δ g⊥) of the CN and C 2H radicals, determined by analysis of high resolution ESR spectra of the radicals in Ar and Kr matrices at 4K, support the predicted relation γ = 2 B OΔ g⊥, where γ and B O are the spin doubling and rotational constants. The analysis also shows that CN in Ar at 4 K undergoes a complex motion resulting in a nonaxial spin hamiltonian.

Spin doubling in the observed2Σ+states of AlO

From high-resolution spectra obtained from low-temperature discharges, the spin doubling in several vibrational levels of the x2 Sigma +, B2 Sigma + and D2 Sigma + observed states of AlO have been calculated. The results differ completely, even in sign for B2 Sigma +, from previous determinations. A theoretical attempt is made to calculate the gamma constant for the ground state and the result appears to confirm the authors' experimental value.

Rotational Energies of Linear Polyatomic Molecules in Vibrationally Degenerate Levels of Electronic 2Σ and 3Σ States

Formulas are developed to describe the rotational energy of a linear polyatomic molecule in a 2Σ or 3Σ electronic state, where one or more quanta of a degenerate bending vibration are excited. In 2Σ states the spin doubling and l-type doubling are independent, provided that the rotational constant B is large compared with the spin–rotation interaction constant γ. In 3Σ states the normal triplet splitting patterns (e.g. Schlapp's formulas) are considerably altered by the presence of vibrational angular momentum at low rotational quantum number N, especially when the spin–spin interaction parameter λ is sizeable; however, with increasing rotation, the normal spin and l-type doubling patterns are approached, as the vibrational angular momentum is progressively uncoupled from the molecular axis.

Intensites absolues et forces d'oscillateur de quelques raies des bandes de vibration-rotation 1-0 et 2-1 du radical OH

Line radiancies ( R L ) have been obtained in the 1-0 and 2-1 vibration-rotation bands of the OH radical using a high resolution infrared grill spectrometer, a blackbody and an oxyacetylene flame. From temperature measurements and calculated values of the OH partial pressures in different regions of the flame, the optical path has been derived. Integrated absorption S v'J' vJ and oscillator strength f v'J' vJ have been ded uced for the four components (lambda and spin doubling) of the P branch lines J = 11 through J = 17 in the 1-0 transition and J = 9 through J = 16 in the 2-1 transition. The values | R 0 1| = 3.1 × 10 -2 D and | R 1 2| = 3.9 × 10 -2 D have been obtained for the vibrational matrix elements of the 1-0 and 2-1 bands. Dipole moment coefficients have been calculated. Results have been compared with those of Heaps and Herzberg.

New spectrum of the SiO+ molecule—a correction

A spectrum previously attributed to SiO+ has been shown to be due to SiN. The sign of the spin doubling of the ground state has been determined and more accurate constants obtained than previously.

Rotational analysis of the 0,2 band of the 11BO α system

The 0,2 band of the α system of 11BO has been carefully analyzed under very high resolution and the following constants were obtained (in cm−1):[Formula: see text]The analysis enables the sign and magnitude of the spin doubling constants γν′ of the B2Σ+ state to be obtained.

Doublet splittings in a non-rigid molecule

The effect of centrifugal distortion on the spin doubling of a non-rigid molecule is evaluated for an orbitally non-degenerate state. This model is used to re-determine the molecular constants for the 2A 1 − 2B 1 transition of PH 2.

THE NIGHT-SKY SPECTRUM λλ 5000-6500 A.

view Abstract Citations (29) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS THE NIGHT-SKY SPECTRUM λλ 5000-6500 A. Blackwell, D. E. ; Ingham, M. F. ; Rundle, H. N. Abstract The paper describes a spectrum of the night sky obtained at the cosmic-ray station of Chacaltaya (latitude - 16 , height 17100 feet) at zenith distance 840, using a dispersion of 78 A/mm The spectrum is unusually intense, and in the region XX 5577-6500 fifty-one OH emission lines (some of which are multiple) are identified; the spin doubling of many lines is clearly resolved. A comparison between observed frequencies and frequencies calculated by means of newly derived band origins and rotational constants is given Rotational temperatures are determined, and the absolute intensities of OH lines and the N I emission at X 5199 have been measured The fine structure of the OH emission in the region of Ha is calculated Publication: The Astrophysical Journal Pub Date: January 1960 DOI: 10.1086/146801 Bibcode: 1960ApJ...131...15B full text sources ADS |