Spin-rotation Interaction Constants Research Articles

High-resolution laser spectroscopy of the linear SiC2Si molecule and its astrophysical implications

Small silicon-carbon clusters are important gas-phase constituents of stellar atmospheres, and are thought to play a role as potential seeds of the interstellar dusts formed in the envelopes of evolved carbon stars. Here we present the high-resolution optical spectra of the linear SiC2Si molecule (l-Si2C2) studied via laboratory experiments. The l-Si2C2 molecules are generated in a supersonically expanding planar plasma by discharging a silane-acetylene-argon gas mixture. The optical absorption spectra in the 5000−5300 Å region are recorded using sensitive pulsed cavity ring-down spectroscopy. In total, five optical absorption bands belonging to the $ \tilde{C} ^{3}\Sigma_{u} ^{-} $ – $ \tilde{X} ^{3}\Sigma_{g} ^{-} $ electronic transition system of l-Si2C2 are measured with fully resolved spin splitting fine structures in individual rotational transitions. Accurate spectroscopic constants for both $ \tilde{X} ^{3}\Sigma_{g} ^{-} $ and $ \tilde{C} ^{3}\Sigma_{u} ^{-} $ states of l-Si2C2, including the spin-spin interaction constants and spin-rotation interaction constants, are determined from the experimental spectra, which can be used to simulate these optical bands with different temperatures. Using the determined spectroscopic constants, optical spectra of l-Si2C2 simulated with different rotational excitation temperatures are compared to the stellar spectra of evolved carbon stars V Hya and IRAS 12311−23509, where the triatomic SiC2 are known to be abundant. Tentative assignments of the l-Si2C2 spectral features in the stellar spectra are discussed.

The emission spectroscopy of the [formula omitted] system of the CD radical

The emission spectrum of the 0-0,1-1 and 2-2 bands of the C2Σ+-X2Π system in the CD molecule have been obtained using a stainless steel hollow-cathode lamp with two anodes and filled with a mixture of He buffer gas and CD4. The emission from the discharge was observed with high accuracy dispersive optical spectroscopy using a plane-grating spectrograph and recorded by a photomultiplier tube. In total, 428 transition frequencies belonging to the three bands were precisely measured and rotationally analyzed. The current data were elaborated with the help of precise ro-vibrational and equilibrium ground state parameters reported by Zachwieja et al. (2012) from investigation of the A2Δ-X2Π transition. The spin-rotation interaction constants γv and γD,v of the C2Σ+,v=0,1,2 levels were obtained for the first time. Moreover, the main equilibrium parameters of the third excited state were obtained as follows: Te=31,825.944(12) cm−1, ωe=2078.803(27) cm−1, ωexe=59.558(12) cm−1, Be=7.86810(23) cm−1, αe=0.25315(58) cm−1 and γe=-0.01518(28) cm−1.

High-resolution photoassociation spectroscopy of the6Li213Σg+state

We present experimental observations of seven vibrational levels $v'=20-26$ of the $1^{3}\Sigma_{g}^{+}$ excited state of Li$_2$ molecules by the photoassociation (PA) of a degenerate Fermi gas of $^6$Li atoms. For each vibrational level, we resolve the rotational structure using a Feshbach resonance to enhance the PA rates from p-wave collisions. We also, for the first time, determine the spin-spin and spin-rotation interaction constants for this state. The absolute uncertainty of our measurements is $\pm 0.00002$ cm$^{-1}$ ($\pm 600$ kHz). We use these new data to further refine an analytic potential for this state.

Cavity Ringdown Spectroscopy of PH2 Radical in 465–555 nm

Absorption spectra of jet-cooled PH2 radicals were recorded in the wavelength range of 465–555 nm using cavity ringdown spectroscopy. The PH2 radicals were produced in a supersonic jet by pulsed direct current discharge of a mixture of PH3 and SF6 in argon. Seven vibronic bands with fine rotational structures have been observed and assigned as 000, 2n0, and 2n1 (n = 1–3) bands of the Ã2A1−X̃2B1 electronic transition. Rotational assignments and rotational term values for each band were re-identified, and the molecular parameters including rotational constants, centrifugal distortion constants, and spin-rotation interaction constants were also improved with reasonably high precision. In addition, large perturbations observed in each quantum number of total angular momentum of the a axis level of the excited vibronic states were briefly discussed.

Microwave, High-Resolution Infrared, and Quantum Chemical Investigations of CHBrF2: Ground and v4 = 1 States

A combined microwave, infrared, and computational investigation of CHBrF(2) is reported. For the vibrational ground state, measurements in the millimeter- and sub-millimeter-wave regions for CH(79)BrF(2) and CH(81)BrF(2) provided rotational and centrifugal-distortion constants up to the sextic terms as well as the hyperfine parameters (quadrupole-coupling and spin-rotation interaction constants) of the bromine nucleus. The determination of the latter was made possible by recording of spectra at sub-Doppler resolution, achieved by means of the Lamb-dip technique, and supporting the spectra analysis by high-level quantum chemical calculations at the coupled-cluster level. In this context, the importance of relativistic effects, which are of the order of 6.5% and included in the present work using second-order direct perturbation theory, needs to be emphasized for accurate predictions of the bromine quadrupole-coupling constants. The infrared measurements focused on the ν(4) fundamental band of CH(79)BrF(2). Fourier transform investigations using a synchrotron radiation source provided the necessary resolution for the observation and analysis of the rotational structure. The spectroscopic parameters of the v(4) = 1 state were found to be close to those of the vibrational ground state, indicating that the ν(4) band is essentially unaffected by perturbations.

Millimeter-wave spectroscopy of H2CCD: Tunneling splitting and ortho-para mixing interaction

The H(2)C=CD isotopic species of vinyl radical produced in a supersonic jet expansion by ultraviolet laser photolysis was studied by millimeter-wave spectroscopy. Due to the tunneling motion of the α deuteron, the ground state is split into two components, 0(+) and 0(-). Tunneling-rotation transitions connecting the lower (0(+)) and upper (0(-)) components of the tunneling doublet were observed in the frequency region of 184-334 GHz, including three R- and two Q-branch transitions. Three and two pure rotational transitions in the K(a)=0 and 1 stacks, respectively, were also observed for each of the 0(+) and 0(-) states in the frequency region of 52-159 GHz. Least-squares analysis of the observed frequencies for the tunneling-rotation and pure rotational transitions with well resolved hyperfine structures yielded a set of precise molecular constants, among which the tunneling splitting in the ground state was determined to be ΔE(0)=1187.234(17) MHz, which is 1/14 that for H(2)C=CH. The potential barrier height derived from the observed tunneling splitting by an analysis of the tunneling dynamics using a one-dimensional model is 1545 cm(-1), consistent with the value 1568 cm(-1) obtained for the normal vinyl. The observed spectrum was found to be perturbed by a hyperfine interaction connecting ortho and para levels. The constant for the interaction, which we call the ortho-para mixing Fermi contact interaction, has been determined to be δa(F) ((β))=68.06(53) MHz. This is believed to be the first definite detection of such an interaction. By this interaction the ortho and para states of H(2)C=CD are mixed up to about 0.1%. The constant is more than 1000 times larger than spin-rotation interaction constants that cause ortho-para mixing in closed shell molecules and suggests extremely rapid conversion between the ortho and para nuclear spin isomers of H(2)C=CD.

Absorption spectra of AsH 2 radical in 435–510 nm by cavity ringdown spectroscopy

The absorption spectra of jet-cooled AsH 2 radicals were recorded in the wavelength range of 435–510 nm by cavity ringdown spectroscopy. The AsH 2 radicals were produced by pulsed DC discharge in a molecular beam of a mixture of AsH 3, SF 6, and argon. Seven vibronic bands with fine rotational structures have been identified and assigned as the 0 0 0 , 2 0 n , and 2 1 n ( n = 1–3) bands of the A ∼ 2 A 1 – X ∼ 2 B 1 electronic transition. Based on the previous studies of AsH 2 radical, rotational assignments and rotational term values for each band were obtained, and the molecular parameters including vibrational constants, rotational constants, centrifugal distortion constants, and spin–rotation interaction constants were also determined.

Pure rotational spectra of the CCCF radical

Pure rotational transitions of a new carbon-chain radical CCCF in a supersonic jet have been observed for the first time using a Fourier-transform microwave spectrometer with a pulsed-discharge nozzle. The radical was produced by a pulsed electric discharge in a C(2)H(2) and CF(4) mixture diluted to 0.1% and 0.1% with Ne, respectively. Rotational transitions with spin and hyperfine splittings have been observed in the region from 9.1 GHz for N(K(a)K(c)) = 1(01)-0(00) to 27.3 GHz for N(K(a)K(c)) = 3(03)-2(02). The rotational constant, the spin-rotation interaction constant, and the hyperfine coupling constants due to the F nucleus have been precisely determined from the least-squares analysis, yielding B = 4555.8043(44), gamma(eff) = -7.105(16), b(F,eff) = 368(19), and c(eff) = -284.832(61) MHz. The determined molecular constants were compared with those obtained from high-level ab initio calculations and concluded that the CCCF radical has a bent ground state X(2)A(').

Laser spectroscopy of the [formula omitted]2A′ − [formula omitted]2A′′ system for the HSO radical

Rotationally resolved spectra of the A ˜ 2 A ′ - X ˜ 2 A ″ system for the HSO radical were observed by laser induced fluorescence spectroscopy. The radical was produced in a discharged supersonic jet of a gas mixture of dimethyl disulfide and O 2 diluted in Ar. The observed spectra were assigned to ro-vibronic transitions of the K a ′ ← K a ″ = 0 ← 1, 1 ← 0, and 2 ← 1 subbands of A ˜ ( 00 v 3 ′ ) - X ˜ (0 0 0) with v 3 ′ = 0–8, and those of A ˜ (0 1 3) − X ˜ (0 0 1), yielding the rotational and spin–rotation interaction constants for the excited electronic state. For the vibronic origin band, the band origin and the rotational constants are determined to be T v = 14383.2533(28) cm −1, A = 287316(33), ( B + C)/2 = 16712.8(48), and ( B − C)/2 = 532.0(70) MHz. Dispersed fluorescence spectra of the HSO radical were also observed, where the fundamental vibrational frequencies of the ν 1 and ν 2 modes for the X ˜ state have been determined experimentally for the first time.

Millimeter-wave spectroscopy of CoNO Produced by UV laser photolysis of Co(CO)3NO

The rotational spectrum of cobalt mononitrosyl (CoNO) produced by ultraviolet photolysis of Co(CO)(3)NO was observed in the millimeter-wave region. Seven rotational transitions in the ground state ranging from J = 6-5 to 12-11, with hyperfine splittings due to the Co nucleus (I = 7/2), were detected in a supersonic jet environment, while higher-frequency transitions in the range from J = 29-28 to 35-34 were measured in the ground, nu(1), nu(2), nu(3), and 2nu(2) vibrational states using a free-space absorption cell. It was confirmed from the observed spectral pattern that the CoNO molecule has a linear structure with the electronic ground state of (1)Sigma(+) symmetry. The rotational lines in the 2nu(2)(Sigma) and nu(3) states were observed to be perturbed by Fermi resonance. The equilibrium rotational constant B(e) is determined to be 4682.207(15) MHz. The CoN bond length is derived to be 1.5842 A assuming the NO bond length of 1.1823 A. A large nuclear spin-rotation interaction constant, C(I) = 123.8(11) kHz, was determined, suggesting a (1)Pi electronic excited state lying close to the ground state.

Analysis of the nuclear quadrupole interaction of Disulfur Dichloride, S 2Cl 2

Pure rotational spectra of S 2 35Cl 2 and S 2 35Cl 37Cl have been observed using a Fourier-transform microwave spectrometer. An analysis of the hyperfine structure made by considering the nuclear spin statistics showed that S 2Cl 2 has C 2 symmetry, where the hyperfine splittings due to the two Cl nuclei were analyzed precisely. The nuclear quadrupole coupling constants including the off-diagonal ( χ ab, χ ac, χ bc) components and the nuclear spin–rotation interaction constants associated with the two Cl nuclei have been determined for the first time. We have shown that the nuclear quadrupole interaction plays an important role in the ortho– para mixing.

Hyperfine constants, nuclear magnetic shielding and spin–spin coupling parameters for AgI and CuI

The high-resolution pure rotational spectra of CuI and AgI have been reinvestigated in the frequency range 2.5–18 GHz using microwave Fourier transform spectroscopy. Gaseous samples of the diatomic metal iodides have been obtained by laser ablation of target rods made of suitable solid precursors. Improved rotational parameters, nuclear quadrupolar coupling constants, and spin–rotation interaction constants have been obtained, along with the first reported spin–spin coupling parameters for copper iodide. Information about the anisotropy of nuclear magnetic shielding and the indirect spin–spin coupling in the absence of intermolecular effects are derived from the high-resolution rotational spectroscopic data.

Emission spectroscopy of the B$^{2}{\mathsf \Sigma}^{+}\!\rightarrow \!{\mathsf X}^{2}{\mathsf \Sigma}^{+}$ system of 12C18O+

The emission spectrum of the B2Σ+→ X2Σ+ system of 12C18O+ has been investigated by using conventional spectroscopic techniques. The 0–1, 0–3, 1–2, 1–4 and 2–5 bands were recorded with high resolution (reciprocal linear dispersion was about 0.030–0.040 nm/mm) and spin splitting of the spectral lines has been precisely studied. Approximately 700 transition wavenumbers were measured with an estimated accuracy of 0.005 cm-1. The rotational analysis has been performed and molecular constants, for the ground X2Σ+ and excited B2Σ+ states, have been extracted. In particular, more reliable values of the spin-rotation interaction constants for the \(B^{2}\Sigma^{+}\ (v = 0, 1, 2)\) state were found to be: γ0=2.0415(37)×10-2 cm-1, γ1=1.9495(30)×10-2 cm-1 and γ2=1.8554(59)×10-2 cm-1, respectively. Also new values of the principal equilibrium parameters and vibrational terms values for B2Σ+ and X2Σ+ states have been provided.

Multi-isotopologue analyses of new vibration–rotation and pure rotation spectra of ZnH and CdH

High resolution infrared emission spectra of ZnH, ZnD, CdH, and CdD have been recorded with a Fourier transform spectrometer. The v = 1 → 0 and v = 2 → 1 bands of ZnH, ZnD, CdH, and CdD, as well as the v = 3 → 2 band of ZnD were observed for the X 2Σ + ground electronic state. In addition, new rotational spectra have been recorded for CdH and CdD using a tunable far-infrared spectrometer, and pure rotational transitions in the v = 1 level of the ground state were measured. The new data were combined with the previous data from diode laser infrared spectra and pure rotation spectra of ZnH/ZnD and CdH/CdD available in the literature. The data from all isotopologues were fitted together using a Dunham-type energy level expression for 2Σ + states, and Born–Oppenheimer breakdown correction parameters were obtained. The equilibrium rotational constants ( B e) of 64ZnH, 64ZnD, 114CdH, and 114CdD were determined to be 6.691332(17), 3.402156(7), 5.447074(18), and 2.750761(6) cm −1, respectively, and the associated equilibrium internuclear distances ( r e) are 1.593478(2), 1.593001(2), 1.760098(3), and 1.759695(2) Å, respectively. Simple reduced mass scaling for the spin–rotation interaction constants of ZnH and CdH fully accounted for their isotopologue dependence, and no Born–Oppenheimer breakdown correction was required for these parameters.

Microwave spectra of the 35Cl and 37Cl isotopomers of dichloromethylene: Nuclear quadrupole-, spin–rotation-, and nuclear shielding constants from the hyperfine structures of rotational lines

The rotational spectra of the isotopomers C 35Cl 37Cl and C 37Cl 2 of dichloromethylene in the ground vibronic state were recorded in the range 10–33 GHz using a molecular beam Fourier transform microwave spectrometer. CCl 2 was generated by flash pyrolysis using different precursors. The observed spectra were analyzed to yield rotational and centrifugal distortion constants, as well as the complete Cl nuclear quadrupole coupling tensors and the spin–rotation interaction constants from the hyperfine structure of the rotational lines. With inclusion of data from previous work on the most abundant species C 35Cl 2 [N. Hansen, H. Mäder, F. Temps, Phys. Chem. Chem. Phys. (3) (2001) 50–55.] a refined r 0 structure was determined. The spin–rotation interaction constants of all three isotopomers were used to derive 35Cl and 37Cl principal inertial axis nuclear magnetic shielding components which have not yet been determined by NMR spectroscopy.

Determination of the proton tunneling splitting of the vinyl radical in the ground state by millimeter-wave spectroscopy combined with supersonic jet expansion and ultraviolet photolysis.

The vinyl radical in the ground vibronic state produced in a supersonic jet expansion by 193 nm excimer laser photolysis of vinyl bromide was investigated by millimeter-wave spectroscopy. Due to the proton tunneling, the ground state is split into two components, of which the lower and higher ones are denoted as 0+ and 0-, respectively. Eight pure rotational transitions with Ka = 0 and 1 obeying a-type selection rules were observed for each of the 0+ and 0- states in the frequency region of 60-250 GHz. Tunneling-rotation transitions connecting the lower (0+) and upper (0-) components of the tunneling doublet, obeying b-type selection rules, were also observed in the frequency region of 190-310 GHz, including three R- and six Q-branch transitions. The observed frequencies of the pure rotational and tunneling-rotation transitions were analyzed by using an effective Hamiltonian in which the coupling between the 0+ and 0- states was taken into account. A set of precise molecular constants was obtained. Among others, the proton tunneling splitting in the ground state was determined to be DeltaE0 = 16,272(2) MHz. The potential barrier height was estimated to be 1580 cm(-1) from the proton tunneling splitting, by an analysis using a detailed one-dimensional model. The spin-rotation and hyperfine interaction constants were also determined for the 0+ and 0- states together with the off-diagonal interaction constants connecting the 0+ and 0- states, epsilonab + epsilonba for the spin-rotation interaction and Tab for the hyperfine interaction of the alpha (CH) proton. The hyperfine interaction constants, due to the alpha proton and the beta (CH2) protons, are consistent with those derived from electron spin resonance studies.

Fourier transform millimeter-wave spectroscopy of the ethyl radical in the electronic ground state.

The pure rotational spectrum of the ethyl radical (C2H5) has been detected for the first time with the Fourier transform millimeter-wave spectrometer. The ethyl radical is produced by discharging the C2H5I gas diluted in Ar. The 1(01)-0(00) rotational transition of the ethyl radical is observed in the frequency range from 43,680 to 43,780 MHz. The observed spectrum shows a very complicated pattern of the fine and hyperfine structures of a doublet radical with the nuclear spins of five protons. The fine and hyperfine components are assigned with the aid of measurements of the Zeeman splittings. As a result, the 22 lines are ascribed to the transitions in the ground vibronic state (A2"). The rotational constant, the spin-rotation interaction constant, and hyperfine interaction constants are determined by the least-squares fit. The Fermi contact term of the alpha-proton is determined to be -64.1654 MHz in the gas phase, indicating that the structure of the -CH2 is essentially planar. The present rotational spectroscopic study further supports that the methyl group of the ethyl radical can be regarded as a nearly free internal rotor with a low energy barrier. A few unassigned lines still remain, which may be vibrational satellites of the internal rotation mode.

First observation of the rotational spectrum of the bromomethyl radical, CH2Br

The first high resolution rotational spectrum of the bromomethyl radical in the gas phase has been observed. The radical was produced in a fast flow system by hydrogen abstraction of CH3Br by Cl or F atoms obtained from a 2450 MHz microwave discharge in Cl2 or in CF4, respectively. The rotational, quartic centrifugal distortion constants have been obtained as well as the electron spin–rotation interaction constants. The small positive inertial defect, Δ0 = 0.032 amu A2 deduced from the rotational constants of the CH279Br species clearly indicates that the radical is planar in its ground vibronic state.

Fourier transform millimeter-wave spectroscopy of the deuterated vinyl radical, C2D3

The 101–000 rotational transition of the C2D3 radical in the ground electronic state has been detected for the first time with the Fourier transform millimeter-wave spectrometer. The C2D3 radical is produced by discharging the C2D3Br gas diluted in Ar. Thirty-two fine and hyperfine components of the 101–000 transition are measured in the frequency region around 44.4 GHz. The rotational constant (B+C)/2, the spin-rotation interaction constant, and the hyperfine interaction constants for the s and a states split by the tunneling motion associated with the CDα rocking mode are determined by a least-squares analysis. The energy splitting due to the tunneling motion is discussed on the basis of the hyperfine interactions. The angle between the CDα bond and the a-axis is estimated to be 148.5° from the nuclear quadrupole interaction constant χaa.

High-Resolution Fourier Transform Emission Spectroscopy of the B2Σ+ (v = 0)–X2Σ+ (v = 0) Transition of the PN+ Ion

Ultraviolet emission spectrum of the B2Σ+ (v = 0)–X2Σ+ (v = 0) transition of the PN+ ion has been observed at a resolution of 0.05 cm−1 by a Fourier transform spectrometer. The rotational analysis led to a great improvement of rotational constants in the B2Σ+ (v = 0) and X2Σ+ (v = 0) states as well as to the first determination of centrifugal distortion constants for both levels and spin–rotation interaction constant in the X2Σ+ (v = 0) state. Rotational perturbation in the B2Σ+ (v = 0) state was observed.