Deperturbation Analysis Research Articles

Doppler-free high resolution spectroscopy of carbon disulphide and the effects of a magnetic field

A single-mode autoscan laser spectrometer operating in the ultraviolet in combination with a collimated molecular beam was used to measure high resolution fluorescence excitation spectra of the CS2 V 1B2 ← X 1Σ+ g transition under collision-free conditions, and the effects of a magnetic field were measured. Rotational and vibrational levels were fully resolved, and Zeeman splittings were observed in many of the perturbed lines. The Zeeman interaction was observed to induce new perturbation, which induces new transitions, level splitting, and energy shift. When the magnetic field strength was changed, the magnitude of the interaction, which was observed in the absence of a magnetic field, changed dramatically depending on the energy shifts of the Zeeman components. It is shown that the V 1B2(1Δu) state is mixed with the B2(3A2) component by first-order spin-orbit interaction, and through the mixed component, the Zeeman interaction between the V 1B2(1Δu) and 3A2(3Δu) states is induced. Large Zeeman splittings were observed for most of the background lines of weak intensity, and this demonstrates that the background levels are levels of the 3A2(3Δu) state. The fluorescence decays of single Zeeman components were observed to be single exponential. The lifetimes of the perturbing 3A2(3Δu) levels were determined by deperturbation analysis. Triplet-triplet 3A2(3Δu) → 3B2(3Σ+ u) emission was confirmed. It was demonstrated that the quenching of the V 1B2 → X 1Σ+ g fluorescence by a magnetic field was caused by mixing of the 3A2 state with the V 1B2 state and the resulting increase of triplet-triplet emission. In a time-dependent picture, the intersystem crossing from the 1B2(1Δu) and 3A2(3Δu) states is enhanced by the magnetic field.

Precise Characterization of the B (1/2) and C (3/2) States of XeF from a Deperturbation Analysis of the B → X Spectrum of 136XeF

The B (1/2) and C (3/2) ion-pair excited states of XeF are coupled by the rotational Hamiltonian, producing perturbations in the rotational structure of B → X(2Σ+) transitions involving υ‘ levels <5. Five υ‘ -υ‘ ‘ bands in the B → X emission spectrum of the single isotopomer 136Xe19F are analyzed by a deperturbation model to yield improved spectroscopic parameters (cm-1) for the low-υ regions of the B and C states: For B, ωe = 308.09, ωexe = 1.480, Be = 0.145 29, and αe = 0.000 675; for C, ωe = 345.1, ωexe = 2.10, Be = 0.165 42, and αe = 0.001 48. The C state lies 797 cm-1 below the B state, with Re = 2.473 Å. The electronic perturbative coupling element for B−C interactions is 1.632, which is 6% below the simple Hund's case c-based prediction ( ) and just 3% greater than an estimate obtained from a more elaborate case a approach.

Fourier Transform Spectroscopy of the A′1Π–X1Σ+ System of CaO

The A′1Π–X1Σ+ near-infrared system of CaO was observed for the first time at high resolution using a Fourier transform spectrometer. The A′1Π–X1Σ+ chemiluminescence was excited in a Ca + N2O flame produced in a Broida-type oven. More than 3000 rotational lines, classified into 19 bands involving the A′1Π 0 ≤ v′ ≤ 3 and the X1Σ+ 1 ≤ v" ≤ 7 vibrational levels were measured in the 4000–10000 cm−1 region with a precision of 0.005 cm−1. The X1Σ+ (v = 0, 1) millimeter-wave and X1Σ+ (v = 0–3) infrared data available in the literature were merged with our new electronic data in order to obtain improved Dunham constants for the ground state of CaO. Very peculiar perturbations are observed in the higher vibrational levels of the A′1Π state, so the upper levels of transitions with v′ = 2 and 3 were represented by term values in our least-squares analysis. The interaction of the A′1Π (v ≥ 2) levels with the nearby b3Σ+ (v–2) levels has been detected. An extended set of A′1Π (v = 0–3) data has been obtained which is suitable for use in a future multistate deperturbation analysis of the a3Π ∼ A′1Π ∼ b3Σ+ ∼ A1Σ+ complex of excited states. The new near-infrared spectra of the A′1Π–X1Σ+ transition of CaO also permits the first direct high-resolution linkage between the orange and green systems and the near-infrared bands.

High-resolution laser spectroscopy of YbS: Deperturbation analysis of the A0+–X0+ transition

The A0+–X0+ electronic transition of Yb172S32, Yb174S32, and Yb176S32 has been rotationally analyzed for the first time. Doppler-limited laser excitation spectroscopy with selective detection of fluorescence was used to obtain spectra of the 0–0, 0–1, 1–1, 1–2, 2–2, and 2–3 bands with a measurement precision of approximately 0.003 cm−1. The 2–2 and 2–3 bands were found to be perturbed by a level crossing that occurs in the A0+ υ=2 level. In total, over 1500 line positions have been measured, assigned, and employed in least-squares fits of molecular parameters. The principal deperturbed results for the X0+ state, which arises primarily from the Yb2+(4f14)S2− electronic configuration, are Re=2.3591(2) Å and ωe(174YbS)=366.714(2) cm−1, and for the A0+ state, R0(174YbS)=2.3905(2) Å.

Perturbation in the V 1B2 state of CS2 and the effects of an applied magnetic field

The excitation spectra of the 15V 31 344.9 band of the CS2 V 1B2←X 1Σg+ transition and the changes in these spectra with the application of a magnetic field of up to 12 kG have been measured with sub-Doppler resolution. The radiative lifetimes of rotationally resolved single lines and single Zeeman components were measured under collision-free conditions. All of the fluorescence decays were observed to be of a single exponential. Large Zeeman splittings were observed for many lines. The only symmetry allowed spin–orbit interaction is that of the A23(B2) component with the B21 state. The A23(B2) component has no magnetic moment, but a magnetic moment is induced when it is mixed with the A23(A1,B1) components. The mixing of the A23(B2) and A23(A1,B1) components is facilitated by spin–rotation interaction and the Zeeman interaction. From analysis of the observed Zeeman splittings of the perturbed levels, the A23(B2) component was determined to lie 14 cm−1 below the nearly degenerate A23(A1) and A23(B1) components in the energy region where the 15V band is observed. Irregular energy shifts and splittings of rotational lines were observed, and these were attributed to (a) Coriolis interaction between the V1B2(v′(a1);K=0JM) and V 1B2(v(b2);K=1JM) levels and (b) resonant spin–orbit interaction between the rotational levels V 1B2(v′(a1);KJM) and R 3A2(v(a1);KJM). These interactions become appreciable when two levels lie close in energy. Large Zeeman splittings were observed in case (b). Many vibrational lines with irregular intensity and spacing were observed in each band. These were attributed to (c) Fermi resonance between the vibrational levels in the V 1B2 state and (d) resonant spin–orbit interaction between vibrational levels in the V 1B2 and R 3A2 states. In case (d), large Zeeman splittings were observed for a series of rotational lines in a vibrational band. The background lines were identified from observed Zeeman splittings as the transitions to levels of the R 3A2 state, which are induced by resonant spin–orbit interaction with the levels of the V 1B2 state. The intensity of the excitation spectrum of the V 1B2←X1Σg+ transition was observed to decrease as the magnetic field increases. This was attributed to a mixing of the A23 state with the V 1B2 state and the resulting triplet–triplet emission, which was not detected in this experiment. It was possible to evaluate the lifetime of the radiative triplet–triplet emission via deperturbation analysis of the perturbed lines.

The c 3Σ+, b 3Π, and a 3Σ+ states of NaK revisited

We present new c 3Σ+→a 3Σ+ laser induced fluorescence spectra of the NaK molecule, which clearly indicate that v0=20 is the first vibrational level of the c 3Σ+ state lying above v=0 of B 1Π state. These spectra are used in a multistep deperturbation (B 1Π∼c 3Σ+∼b 3Π) procedure to obtain improved a 3Σ+, b 3Π and c 3Σ+ potential energy curves. The deperturbation analysis is confirmed by the calculated electronic B 1Π∼c 3Σ+ and c 3Σ+∼b 3Π spin–orbit matrix elements obtained from many-body multipartitioning perturbation theory employing the relativistic effective potential method.

Near-infrared laser absorption spectroscopy of the CS + cation

The (1, 0) band of the A 2 Π– X 2 Σ + transition of the CS + cation has been measured in absorption at Doppler-limited resolution, between 12 400 and 13 000 cm −1. The spectrum was recorded using differential velocity modulation detection and a Ti: sapphire laser as the near-infrared light source. The v=1 A 2 Π upper state of the band is perturbed by the v=10 level of the ground state. A deperturbation analysis using >300 rotational lines was carried out to derive accurate ground- and upper-state parameters. The ground-state rotational and fine-structure constants are in very good agreement with those from a Fourier transform emission study in which the ground-state constants were derived from combination differences.

Electronic nonadiabaticity in highly vibrationally excited O2(X 3Σg−): Spin-orbit coupling between X 3Σg− and b 1Σg+

We report full quantum-state-resolved spectra of highly vibrationally excited O2(X 3Σg−,v=26–31). In addition to providing high precision molecular constants for several new vibrational levels, we observe a local spectral perturbation of X 3Σg−(v=28). We present a deperturbation analysis of the observed spectra and assign the perturber to b 1Σg+(v=19). We predict a crossing between the b 1Σg+ and X 3Σg− state at an internuclear separation R=2.45±0.1 Å, somewhat further extended and higher in energy than the outer classical turning point of O2(X 3Σg−,v=28). Using the appropriate vibrational overlap integral, we are able to determine the spin–orbit interaction between these two electronic states, which is 200±20 cm−1 in the vicinity of the crossing. These results suggest that the collision dynamics of highly vibrationally excited O2(X 3Σg−) may involve excited potential surfaces. Furthermore, they imply that present theoretical approaches to the O4 problem, which use a single potential surface, may not be adequate. Possible implications regarding nonequilibrium models of stratospheric ozone formation and the dynamics of the O+O3→2O2 reaction are discussed.

Spin-orbit coupling in the D1Pi d3Pi complex of 23Na39K

A comprehensive deperturbation analysis is made of the singlet—triplet D 1Δ ∼ d3Δ complex of the 23Na39K molecule. The deperturbation model takes into account direct spin—orbit coupling between the singlet and triplet states plus a spin—rotational interaction between different Ω components of the triplet state. The direct inversion procedure provides a self-consistent set of the Dunham molecular constants for both states and for the matrix elements of the spin—orbit interaction. The deperturbation analysis is supported by electronic structure calculations performed in the framework of the relativistic effective potential method combined with many-body multipartitioning perturbation theory. The theoretical spin—orbit matrix elements agree well with their experimental counterparts.

Spin—orbit coupling in the D 1Δ ∼ d 3Δ complex of 23Na39K

A comprehensive deperturbation analysis is made of the singlet—triplet D 1Δ ∼ d3Δ complex of the 23Na39K molecule. The deperturbation model takes into account direct spin—orbit coupling between the singlet and triplet states plus a spin—rotational interaction between different Ω components of the triplet state. The direct inversion procedure provides a self-consistent set of the Dunham molecular constants for both states and for the matrix elements of the spin—orbit interaction. The deperturbation analysis is supported by electronic structure calculations performed in the framework of the relativistic effective potential method combined with many-body multipartitioning perturbation theory. The theoretical spin—orbit matrix elements agree well with their experimental counterparts.

Velocity modulated laser absorption spectroscopy of TiCl+

Velocity modulated laser absorption spectrum of the TiCl+ molecular ion was recorded in the yellow-green spectral region. The ions were generated in a 25 kHz ac discharge through flowing samples of TiCl4 in Ar. The [17.9]3Δ−X3Φ and [17.9]3Δ−(1)3Δ band systems of TiCl+ were recorded and analyzed. We report the results of a deperturbation analysis of the X3Φ and (1)3Δ states. A multiconfiguration ligand field calculation was used to account for the observed electronic states of TiCl+.

Analysis of the C 2Π r, ν = 0 ∼ 4Σ + and 2Σ − perturbations of the AlO radical

A deperturbation analysis is made for the 0-0 band of the AlO(C 2Π r − X 2Σ +) transition measured by Singh and Saksena [Can. J. Phys. 61 (1983) 1347]. The states perturbing the C 2Π r, ν = 0 level are assigned to 4Σ + and 2Σ −. The molecular constants for the C 2Π r, ν = 0 state and the perturbing levels are determined by a deperturbation analysis. The vibrational quantum numbers of the perturbing 4Σ + and 2Σ − level are estimated to be 4 and 0, respectively.

Deperturbation Analysis of the [18.5]1-X0+ System and the Electronic Structure of ReN: A Laser Induced and Dispersed Fluorescence Study

We report a deperturbation analysis of the [18.5]1-X0+ system of ReN. Heterogeneous Ja uncoupling involving a “dark” (Ω = 2) state is responsible for the observed perturbation. For the (0−0) band located near 540 nm, extra branches as well as an irregular energy level pattern are observed. For the (1−0) band near 510 nm, although the observed spectrum appears regular, the B‘ value deduced from a previous analysis is not consistent with values associated with other vibrational levels. A careful reexamination of this band, using dispersed fluorescence to filter the laser induced fluorescence (LIF) spectra, allowed us to separate the “bright” and “dark” state contributions to the original LIF spectrum. In fact two spectra can be obtained, corresponding mainly either to the “bright” or to the “dark” excited states. Rotational analyses have been carried out for both of these (1−0) bands and confirm the deperturbation analysis of the (0−0) bands. Excited state lifetimes have been measured for individual ro-vibr...

Doppler-free spectroscopy of KLi

The B 1∏–X 1∑+ band system of the 39K7Li molecule was investigated by Doppler-free polarization spectroscopy in a heat-pipe oven. Precise molecular constants for levels v=0–3 in the ground X 1∑+ state and levels v=0–2 in the excited B 1∏ state were determined. The e-parity components in all three vibrational levels of the B state were found to be subject to rotational perturbations, assigned to interaction with the C 1∑+ state. The deperturbation analysis provided preliminary constants of the perturbing C state and values of the coupling matrix elements.

Lifetime measurements of selectively excited rovibrational levels of the V 1B2 state of CS2

The radiative lifetimes of selectively excited rovibrational levels of the V 1B2 state of the CS2 molecule have been measured under collision-free conditions in a cold molecular beam using a pulse-modulated frequency-doubled single-mode cw dye laser. Pure exponential fluorescence decays were found for all excited levels. The lifetimes, scattering considerably in the range of 2–13 μs, give evidence of interactions of the V 1B2 state with background states. A deperturbation analysis performed for rotational levels involved in local two-level interactions yields detailed quantitative information on the V 1B2 state and on the background levels. It is shown that these levels represent rovibrational levels of the B2(3A2) state and highly excited rovibrational levels of the X 1Σg+ electronic ground state. The coupling mechanisms are: (1) the spin–orbit interaction between the V 1B2 state and the B2(3A2) state where the latter is coupled to the X 1Σg+ ground state by spin–orbit/vibronic and spin–orbit/Coriolis interaction and (2) the Coriolis coupling of the V 1B2 state to the X 1Σg+ ground state. Further sources of perturbations are the spin-uncoupling in the 3A2 state and the Renner–Teller coupling of the V 1B2 state to the 1A2 state. From the measured radiative lifetimes of the background states information on the electronic structure of the CS2 molecule is gained.

New bands of the MgO A1Π-X1Σ+ and a3Π0,1-X1Σ+ systems by Faraday laser magnetic resonance spectroscopy

Abstract Extended measurements are reported for rovibronic transitions between the strongly mixed low-lying X1Σ+, a3Π and A1Π electronic states of the MgO molecule in the 1640–3510 cm−1 region. The measurements were made with the Faraday laser magnetic resonance (LMR) technique utilizing a CO laser and a CO overtone laser. The new observed lines include the A1Π-X1Σ+ (0–0, 0–1, 1–1, 1–2, 1–3, 2–2, 2–4, 3–3) bands as well as the much weaker a3Π0.1–X1Σ+ (0–0, 1–0) intercombination bands. The present highly precise LMR data provide a basis for performing an extensive deperturbation analysis including the spin-orbit, orbit-rotation and Zeeman interactions between the rovibronic levels of the X1Σ+, a3Π and a1Π states. Thereby the present data are combined with reliable earlier experimental results, in particular for the transitions involving higher lying vibronic states, in order to obtain the effective deperturbed molecular constants and perturbation parameters for the three lowest lying electronic states of MgO to as high an accuracy as possible. The absolute standard deviation of the LMR data is 6 × 10−4 cm−1 (18 MHz), which is in accord with the accuracy of our measurements. The set of deperturbed molecular parameters reproduces all measured lines with an overall standard deviation of 0·87 relative to the experimental uncertainties. For perturbations such as spin-orbit interaction there is good agreement with the predictions of large scale ab initio calculations.

New bands of the MgO A 1 Π-X 1 Σ + and a 3 Π 0,1 -X 1 Σ + systems by Faraday laser magnetic resonance spectroscopy

Abstract Extended measurements are reported for rovibronic transitions between the strongly mixed low-lying X1Σ+, a3Π and A1Π electronic states of the MgO molecule in the 1640–3510 cm−1 region. The measurements were made with the Faraday laser magnetic resonance (LMR) technique utilizing a CO laser and a CO overtone laser. The new observed lines include the A1Π-X1Σ+ (0–0, 0–1, 1–1, 1–2, 1–3, 2–2, 2–4, 3–3) bands as well as the much weaker a3Π0.1–X1Σ+ (0–0, 1–0) intercombination bands. The present highly precise LMR data provide a basis for performing an extensive deperturbation analysis including the spin-orbit, orbit-rotation and Zeeman interactions between the rovibronic levels of the X1Σ+, a3Π and a1Π states. Thereby the present data are combined with reliable earlier experimental results, in particular for the transitions involving higher lying vibronic states, in order to obtain the effective deperturbed molecular constants and perturbation parameters for the three lowest lying electronic states of M...

New bands of the MgO A1Π-X1Σ+ and a3Π0,1-X1Σ+ systems by Faraday laser magnetic resonance spectroscopy

Abstract Extended measurements are reported for rovibronic transitions between the strongly mixed low-lying X1Σ+, a3Π and A1Π electronic states of the MgO molecule in the 1640–3510 cm−1 region. The measurements were made with the Faraday laser magnetic resonance (LMR) technique utilizing a CO laser and a CO overtone laser. The new observed lines include the A1Π-X1Σ+ (0–0, 0–1, 1–1, 1–2, 1–3, 2–2, 2–4, 3–3) bands as well as the much weaker a3Π0.1–X1Σ+ (0–0, 1–0) intercombination bands. The present highly precise LMR data provide a basis for performing an extensive deperturbation analysis including the spin-orbit, orbit-rotation and Zeeman interactions between the rovibronic levels of the X1Σ+, a3Π and a1Π states. Thereby the present data are combined with reliable earlier experimental results, in particular for the transitions involving higher lying vibronic states, in order to obtain the effective deperturbed molecular constants and perturbation parameters for the three lowest lying electronic states of MgO to as high an accuracy as possible. The absolute standard deviation of the LMR data is 6 × 10−4 cm−1 (18 MHz), which is in accord with the accuracy of our measurements. The set of deperturbed molecular parameters reproduces all measured lines with an overall standard deviation of 0·87 relative to the experimental uncertainties. For perturbations such as spin-orbit interaction there is good agreement with the predictions of large scale ab initio calculations.

Rotation-Electronic Deperturbation Analysis of the 4f 6s Configurational States of CeO

Rotation-electronic interactions between states of the 4 f 6s configuration of CeO, mediated by the operator -B(R)(Ĵ+·Ĵ−a + Ĵ−·Ĵ+a), have been calculated. Second-order perturbation theory was used to account for the effect of heterogeneous interactions on the rotation constants within a single configuration. Eigenvectors from a ligand field theory calculation were used to evaluate these interactions. The results demonstrate the capability of the ligand field model to predict electronic-rotational interactions, and they illustrate the value of these interactions for uncovering the atomic-ion quantum numbers that are not readily determined for molecules in the strong spin-orbit coupling limit [Hund′s case (c)].

Fast-Ion-Beam Laser Spectroscopy of the B2Σ +- X2Σ + and B2Σ +- A2Π Systems of SiO +: Deperturbation Analysis

We have completed a deperturbation analysis of a set of measurements in SiO + including seven bands of the B 2Σ +- X 2Σ + system, the (2, 0) Ω = 1 2 sub-band of the B 2Σ +- A 2Π system, and fine structure intervals of the ν = 0 level of the X 2Σ + state. The pattern of perturbations in the B- X system shows that the assignments of vibrational levels in the A 2Π state made in earlier photoelectron spectroscopy work are incorrect. Deperturbed molecular constants for the three electronic states have been derived.