Abstract
We studied the molecule LiRb in the gas phase with high resolution by Fourier-transform spectroscopy of laser induced fluorescence. The spectra were assigned to transitions between the ground state X^{1}Σ^{+} and B^{1}Π or D^{1}Π states and showed perturbations. For levels with e symmetry the coupling to the nearby state C^{1}Σ^{+} was included in the analysis by means of coupled channel calculations. The evaluation gives potential energy curves for all three electronic states and the coupling functions for B-C coupling, which are related to the expectation value of the electronic orbital angular momentum operator L^{+} or L^{−}. The same coupling between C and D states is considered, but is not yet as fixed as in the case B-C because of lack of data. The model was extended to include the Λ-doubling by distant electronic states through effective q-parameters, but their interpretation is incomplete because of several possible perturbing states and too few data.
This work was supported by the Deutsche Forschungsgemeinschaft in the frame of the Cluster of Excellence QUEST. A.P. acknowledges partial support from the Bulgarian National Science Fund Grant Nos. VUF 20206, VUI 301/07 and the Sofia University Grant Nos. 1422008, 1722009, and E.T. acknowledges the support from the Minister of Science and Culture of Lower Saxony, Germany, by providing a Niedersachsenprofessur.
I. INTRODUCTION
II. EXPERIMENTAL DATA
III. B^{1}Π STATE
IV. D^{1}Π STATE
V. CONCLUSION
Key Topics
- Ground states
- 14.0
- Parity
- 7.0
- Data analysis
- 5.0
- Laser induced fluorescence
- 5.0
- Ab initio calculations
- 4.0
F03H3/00
Figures
(a) Potential energy curves for selected electronic states of LiRb (ab initio calculations from Ref. ^{ 3 } ). (b) A typical spectrum of the LIF from the D^{1}Π state following the laser excitation X(4,57)-D(1,58). For suppressing the scattered laser light a color glass filter was applied.
(a) Potential energy curves for selected electronic states of LiRb (ab initio calculations from Ref. ^{ 3 } ). (b) A typical spectrum of the LIF from the D^{1}Π state following the laser excitation X(4,57)-D(1,58). For suppressing the scattered laser light a color glass filter was applied.
Gerö plots representing the distribution of the experimental data for all four isotopologues in LiRb for the B^{1}Π state (a) and the D^{1}Π state (b).
Gerö plots representing the distribution of the experimental data for all four isotopologues in LiRb for the B^{1}Π state (a) and the D^{1}Π state (b).
Perturbations in v′ = 0 (left) and v′ = 2 (right) for the state B^{1}Π in LiRb.
Perturbations in v′ = 0 (left) and v′ = 2 (right) for the state B^{1}Π in LiRb.
Derived potentials for states B^{1}Π, C^{1}Σ^{+}, and D^{1}Π and their coupling functions b _{ B }(R) and b _{ D }(R) according Eq. (1) .
Derived potentials for states B^{1}Π, C^{1}Σ^{+}, and D^{1}Π and their coupling functions b _{ B }(R) and b _{ D }(R) according Eq. (1) .
Deviations of the f-parity levels for v′ = 4 of the D^{1}Π state from their predictions by the fitted potential curve (upper) and their actual observation in the experimental spectra (lower) where doubled lines are observed. The second line with label J ^{′} = 94 is very strong and thus overshoots in the drawing. The asymmetric line shape is an artifact of the Fourier transformation due to the large signal amplitude.
Deviations of the f-parity levels for v′ = 4 of the D^{1}Π state from their predictions by the fitted potential curve (upper) and their actual observation in the experimental spectra (lower) where doubled lines are observed. The second line with label J ^{′} = 94 is very strong and thus overshoots in the drawing. The asymmetric line shape is an artifact of the Fourier transformation due to the large signal amplitude.
Histogram showing the distribution of the residuals E ^{ obs } − E ^{ calc } for the term energies of the D state. The solid line is a Gaussian fit resulting in a width of 0.011 cm^{−1}.
Histogram showing the distribution of the residuals E ^{ obs } − E ^{ calc } for the term energies of the D state. The solid line is a Gaussian fit resulting in a width of 0.011 cm^{−1}.
Tables
The potential coefficients and derived molecular constants for state B^{1}Π in ^{7}LiRb. The potential energy is calculated with respect to the minimum of the ground state X^{1}Σ^{+}, the dispersion coefficients are adjusted for continuous connection to the respective excited atomic asymptote.
The potential coefficients and derived molecular constants for state B^{1}Π in ^{7}LiRb. The potential energy is calculated with respect to the minimum of the ground state X^{1}Σ^{+}, the dispersion coefficients are adjusted for continuous connection to the respective excited atomic asymptote.
The potential coefficients and derived molecular constants for the state C^{1}Σ^{+} in ^{7}LiRb. The potential energy is calculated with respect to the minimum of the ground state X^{1}Σ^{+}, the dispersion coefficients are adjusted for continuous connection to the respective excited atomic asymptote.
The potential coefficients and derived molecular constants for the state C^{1}Σ^{+} in ^{7}LiRb. The potential energy is calculated with respect to the minimum of the ground state X^{1}Σ^{+}, the dispersion coefficients are adjusted for continuous connection to the respective excited atomic asymptote.
Coupling parameters for b _{ B }(R) between states B^{1}Π and C^{1}Σ^{+} in ^{7}LiRb and effective Λ-doubling parameters of q _{ e/f }(R) for coupling of distant states with respect to state B^{1}Π.
Coupling parameters for b _{ B }(R) between states B^{1}Π and C^{1}Σ^{+} in ^{7}LiRb and effective Λ-doubling parameters of q _{ e/f }(R) for coupling of distant states with respect to state B^{1}Π.
Pointwise representation of the potential energy curve for the D^{1}Π state of ^{7}LiRb. For interpolation a natural cubic spline through all the listed points should be used. ^{ 17 } The long range expansion (Eq. (5) ) with coefficients C _{6} and C _{8} taken from Ref. ^{ 16 } and C _{10} constructed for continuous connection starts at R _{ o } = 15.127 Å.
Pointwise representation of the potential energy curve for the D^{1}Π state of ^{7}LiRb. For interpolation a natural cubic spline through all the listed points should be used. ^{ 17 } The long range expansion (Eq. (5) ) with coefficients C _{6} and C _{8} taken from Ref. ^{ 16 } and C _{10} constructed for continuous connection starts at R _{ o } = 15.127 Å.
Comparison of molecular parameters determined from spectroscopy and ab initio calculations. ^{ 3 } The vibrational frequencies are for ^{7}Li^{85}Rb ^{ a } .
Comparison of molecular parameters determined from spectroscopy and ab initio calculations. ^{ 3 } The vibrational frequencies are for ^{7}Li^{85}Rb ^{ a } .
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