Vibration-rotation transition probabilities in CH+ and CD+

Vibrational dipole matrix elements and radiative transition probabilities have been evaluated from electric dipole moment functions for the X¹Σ⁺ states of CH⁺ and CD⁺, which were calculated from highly correlated electronic wavefunctions. The dipole moments in ν = 0 amount to 1.679 D (CH⁺) and 1.313 D (CD⁺), respectively. In comparison to other molecular ions the infrared transition probabilities are found to be rather small. For instance, the Einstein coefficient of spontaneous emission A¹₀ amounts to 1.63 s⁻¹ (CH⁺) and 0.19 s⁻¹ (CD⁺). Dipole moment functions of the neutral CH species in the X²Π and a⁴ Σ⁻ states have also been calculated and are compared with previous theoretical functions.     

Ab initio calculations of infrared transition probabilities in the electronic ground states of AlF and AlF+

Electric dipole moment functions and radiative transition probabilities have been calculated for the electronic ground states of AlF and AlF⁺ from highly correlated CEPA electronic wavefunctions. The dipole moments inv = 0 are calculated to be 1.56 D (experimental value is 1.53 ±0.1 D) for AlF and 5.49 D for AlF⁺. Intense transitions in the microwave and infrared spectral region are predicted for both species.     

Ab initio calculations of infrared transition rates in the ground states of BF and BF+

Electric dipole moment functions and radiative transition rates have been calculated for the X¹Σ⁺ state of BF and the X²Σ⁺ state of BF⁺ from MC SCF wavefunctions. Both are predicted to be strong emitters in the infrared. For BF⁺ the electronically excited ²Σ⁺ state, corresponding to the configuration 1σ²2σ²3σ²4σ5σ²1π⁴, is calculated to be bound, whereas the A ^Π state is repulsive.     

Rate constants of the near-resonant E-E energy exchange processes SeS(b0+) + O2(X3Σg−) ⇌ SeS(X10+) + O2(a1Δg)

SeS radicals generated in a fast flow system were excited to their b0⁺, ν' = 0 vibronic state by absorption of Raman-shifted dye laser pulses at 1280 nm. From time-resolved measurements of the b0⁺ → X₁0⁺ fluorescence as a function of added gas pressure, the radiative lifetime of the b0⁺ = 0 state (τ₀ = 400 ± 100 μs) and quenching rate constants for H₂, D₂, N₂, CO, O₂, and CO₂ were deduced. Quenching of SeS(b0⁺, ν'= 0) by O₂ is attributed to the near-resonant electronic- to-electronic energy-transfer process (1), SeS(b0⁺, ν'₁ = 0) + O₂(X³Σ_g⁻, ν″₁ = 0) ⇌ SeS(X₁0⁺, ν″_f = 0) + O₂(a¹Δ_g, ν'_f = 0)−77 cm⁻¹, for which (k₁ = (1.4±0.3) × 10⁻¹² cm³ s⁻¹ was obtained. On the assumption of detailed balancing, k₋₁ was calculated to be (3.0 ± 0.7) × 10⁻¹²cm³ s⁻¹.     

Theoretical evaluation of the radiative lifetimes of LiCs and NaCs in the A<Superscript>1</Superscript>Σ<Superscript>+</Superscript> state

Calculations of the adiabatic potential energy curves and the transition dipole moments between the ground (A¹Σ⁺) and the first excited (A¹Σ⁺) states have been determined for the LiCs and NaCs molecules. The calculations are performed using an ab initio approach based on non-empirical pseudopotentials for Cs⁺, Li⁺ and Na⁺ cores, parameterized l-dependent polarization potentials and full configuration interaction calculations. The potential energy curves and the transition dipole moment are used to estimate the radiative lifetimes of the vibrational levels of the A⁺Σ⁺ state using the Franck–Condon (FC) approximation and the approximate sum rule method. The radiative lifetimes associated with the A⁺Σ⁺ state are presented here for the first time. These data can help experimentalists to optimize photoassociative formation of ultracold molecules and their longevity in a trap or in an optical lattice.     

Theoretical and experimental studies of radiative lifetimes of excited electronic states in CO

The electronic dipole transition moment functions of the A ²Π-X ²Σ⁺, B ²Σ⁺-X ²Σ⁺ and B ²Σ⁺-A ²Π transitions and the dipole moment function of the X ²Σ⁺ state of CO⁺ have been calculated using large contracted CI wavefunctions. The computed transition moment functions together with experimental potential energy curves were used to obtain radiative lifetimes of the excited electronic states B ²Σ⁺ and A ²Π. Radiative lifetimes of vibrational levels of the X ²Σ⁺ state were derived from the calculated dipole moment function. The high-frequency deflection technique was used to obtain radiative lifetimes of the ν′ = 0, 1,2 and 3 vibrational levels of the B ²Σ⁺ state and also radiative lifetimes of individual rotational levels of ν′ =0. The calculated radiative lifetimes are shorter than the measured ones by about 10%. The experimental ν′ dependence is reproduced by theoretical calculation. The calculated radiative lifetimes for the A ²Π state are in excellent agreement with lifetimes measured with an ion trap technique.     

Ab Initio Diabatic energies and dipole moments of the electronic states of RbLi molecule

For all states dissociating below the ionic limit Li^? Rb⁺, we perform a diabatic study for ¹Σ⁺ electronic states dissociating into Rb (5s, 5p, 4d, 6s, 6p, 5d, 7s, 4f) + Li (2s, 2p, 3s). Furthermore, we present the diabatic results for the 1–11 ³σ, 1–8 ^1,3Π, and 1–4 ^1,3Δ states. The present calculations on the RbLi molecule are complementary to previous theoretical work on this system, including recently observed electronic states that had not been calculated previously. The calculations rely on ab‐initio pseudopotential, core polarization potential operators for the core‐valence correlation and full valence configuration interaction approaches, combined to an efficient diabatization procedure. For the low‐lying states, diabatic potentials and permanent dipole moments are analyzed, revealing the strong imprint of the ionic state in the ¹Σ⁺ adiabatic states. The transition dipole moment is used to evaluate the radiative lifetimes of the vibrational levels trapped in the 2 ¹Σ⁺ excited states for the first time. In addition to the bound–bound contribution, the bound–free term has been evaluated using the Franck–Condon approximation and also exactly added to the total radiative lifetime. © 2013 Wiley Periodicals, Inc.     

Precision measurements of hyperfine predissociation in I2 vapor using a two-photon resonant scattering technique

A two-photon resonant scattering technique is used to measure natural linewidths of individual hyperfine components of the ν′ = 43,J′ = 12 and 16 rovibrational levels in the I₂ B state (³π_ou⁺). Differences in the linewidths due to hyperfine predissociation are precisely determined. The predissociation constants and the radiative linewidth for ν′ = 43 are found to be [a_ν′]² = 3.36 ± 0.09 kHz, [c_ν′]² = 4.67 ± 0.51 Hz and Γ_r = 51 ± 4 kHz, respectively.     

Dipole moments,transition moments,oscillator strengths,radiative lifetimes,and overtone intensities for CH and CH+ as computed by quasi-degenerate many-body perturbation theory

The correlated, size-consistent, ab initio effective valence-shell dipole operator (μ^v) method is used to calculate dipole moments and transition dipole moments of the CH molecule and transition dipole moments of the CH⁺ ion as a function of internuclear distance. The dipole and transition dipole moments computed here compare well with those of other accurate ab initio methods. The transition dipole moments are then used to calculate oscillator strengths and radiative lifetimes for the A → X and B → A transitions of the CH⁺ ion and the A → X transition of the CH molecule. Comparisons are made with the best available theoretical and experimental lifetimes. Finally, the CH ground-state dipole moment function is used to evaluate overtone intensities and to examine simple models of the CH overtone intensities in polyatomic molecules.     

Level energies and infrared radiative lifetimes of the muonic molecule Heμ+

Energies and radiative lifetimes are calculated for all bound and quasibound levels of the positive muon molecular ion Heμ⁺, together with the tunneling predissociation lifetimes of its quasibound levels. The radiative lifetimes obtained are much longer than the positive muon decay lifetime, so spontaneous (“infrared”) emission will not be a useful diagnostic for the presence of Heμ⁺ or the analogous molecular ions formed by the heavier inert gas atoms.     

Radiative lifetimes of the B1Π11 states of Li2

Model potential calculations of the B¹Π_uX¹Σ⁺_g transition dipole moment are used in conjunction with the empirical potential energy curves of Vidal and Hessel to calculate the radiative lifetimes of the vibrational levels of the B¹Π_u state. The lifetimes are nearly independent of the vibrational quantum number with a value between 8 and 9 ns.     

Vibrational radiative lifetimes in H2Se and HCS−

Vibrational dipole matrix elements and radiative transition probabilities for H₂Se and HCS⁻ have been evaluated from theoretical three-dimensional electric dipole moment and potential energy functions. The radiative lifetimes of the (v=1,J=0) levels of HCS⁻ have been calculated to be 3.5 ms (CH stretch), 172 ms (HCS bend) and 785 ms (CS stretch), and in H₂Se to be 122 ms (symmetric stretch), 1045 ms (bend) and 101 ms (asymmetric stretch). The lifetimes of higher vibrational states with no extensive mode-mixing decrease with increasing vibrational quantum number and vary in a mode-specific way.     

Fluorescence lifetimes and predissociation of the A3Π state of SH+

The high frequency deflection (HFD) technique has been used to obtain fluorescence lifetimes of the SH⁺ A³Π state. The A³Π?X³∑^? electronic transition moment function has been calculated with the complete active space SCF(CASSCF) method. Radiative lifetimes calculated with this transition moment function are compared with measured lifetimes and found to be in good agreement (τ_exp(v′=0)=1.4±0.3 µs; τ_calc=1.6 µs). Deviations between measured and calculated lifetimes forv′=0,J′ ≥ 15 andv′=1,J′=1?7 are interpretated as due to a predissociation caused by a repulsive⁵∑^? state. A simple model, based on a perturbation approach to the predissociation, is used to obtain quantitative estimates of predissociation rates. These calculated rates are in reasonable agreement with the predissociation rates that are inferred from the measured and calculated lifetimes.     

Spectra and structure of small ring compounds: XXIX. Microwave spectrum of γ-butyrolactone

The microwave spectrum of γ-butyrolactone has been recorded from 12.4 to 40.0 GHz. Both A-type and B-type transitions were observed. The R-branch assignments have been made for the ground state and the first two excited states of the ring-puckering and the first excited state of the ring twisting modes. It is shown that the ring skeleton is non-planar from the magnitude of the μ_c component of the dipole moment as well as from the value of I_c?(I_a+I_b). From the relative intensity measurements of the ground and the excited state, the ring twisting mode appears to be governed by a double minimum potential. The dipole moment was determined to be 4.27±0.03 D with components of μ_a = 4.04±0.03 D, μ_b = 1.42±0.03 D, μ_c = 0.33±0.02 D. From an investigation of the Raman spectrum of the gas, the ring puckering vibration was found to have a frequency of 148 cm^?1, whereas the ring twisting mode was found at 225 cm^?1.     

Calculation of the absolute infrared intensities for the 0−1, 0−2 and 1−2 vibration-rotation transitions in the ground state of no+

The absolute infrared intensities of the 0?1, 0?2 and 1?2 vibration-rotation bands in the ¹Σ⁺ ground state have been calculated from first principles. The dipole moment function for NO⁺ was determined in the region of the equilibrium internuclear separation by an accurate multi-configuration self-consistent-field procedure. The dipole matrix elements over vibration states were solved exactly using numerical techniques. The ratio of the calculated integrated absorption coefficients for the fundamental and first overtone (88.8 cm^?2 atm^?1 and 0.6 cm^?2 atm^?1, respectively, at 273.16°K) is in reasonable agreement with an estimate based on observation of these bands in NO⁺ at high altitudes in the upper atmosphere.     

A quantum chemical study of the infrared absorption intensities of the isolectronic C3v systems NH3, H3O+ and CH−3

The dipole moment derivatives and the infrared absorption intensities for the isoelectronic, isostructural species NH₃, H₃O⁺ and CH⁻₃, calculated by ab initio quantum methods within the double harmonic approximation, are reported. The calculations were performed at the SCF, CI and CPA″ levels of theory using basis sets of triple zeta+two polarization functions quality. For the ions H₃O⁺ and CH⁻₃, in the absence of adequate experimental information, the calculations are fully ab initio, since the equilibrium geometries as well as the force constants had to be computed. The applicability of the harmonic treatment to systems with inversion potentials is discussed, especially with regard to H₃O⁺. The dipole moment derivatives of the three systems show interesting, regular trends in accordance with the amount of electronic charge associated with the hydrogen atoms.     

Potential energy curves and spectral properties for electronic states of F2 and F+2

Potential energy (PE) curves for the Rydberg states of F₂, and for the ground and lowest two electronic states each of symmetry ²Π_g,u, ²Δ_g,u and ²Σ^±_g,u of F⁺₂, have been obtained using modest-sized configuration-interaction calculations. These PE curves have been used to calculate spectroscopic constants for the electronic states and the results agree reasonably well with the limited experimental and theoretical results previously reported. The theoretical PE curves for the Rydberg states of F₂ are found to be strongly perturbed by valence-Rydberg-ionic interactions and these perturbations appear to be responsible for certain features in recently reported electron energy-loss spectra in F₂. The corresponding electronic wavefunctions have been used to calculate the electronic transition moment, as a function of the internuclear distance, for dipole-allowed transitions between the lowest excited electron state of each symmetry and the appropriate ground electronic state. The radiative emission probabilities, natural lifetimes, and absorption oscillator strengths, for each band system, are also reported here. The predicted lifetimes for vibrational levels of the A ²Π_u of electronic state in F⁺₂ vary from 1.3–1.5 μs and agree reasonably well with the single available set of measurements. The predicted radiative lifetimes for the higher electronic states of F⁺₂ are substantially longer and fall into the range 5–100 ms.     

Radiative lifetime of CO+ (X2∑+, ν) ions

The radiative relaxation of CO⁺(X²∑⁺, ν) ions produced by ionization of CO and of OCS with 70 eV electrons has been investigated using the monitor ion technique in a triple FT ICR spectrometer. Since the monitor reaction is exothermic for ν ≥ 1, the experimental lifetimes, 170 ms for CO⁺ from CO and 210 ms for CO⁺ from OCS, should correspond to the overall decay rate of ν ≥ 2 with a small contribution of ν = 1.These values being much larger than the theoretical lifetime of ν = 1 (128.5 ms), computer-simulated overall lifetimes for ν ≥ 1 and ν ≥ 2 have been determined using theoretical lifetimes calculated by Rosmus and Werner and a vibrational population deduced from photoelectron spectroscopy of CO with 40.8 eV photons (Gardner and Samson). The computer-simulated lifetimes, 250 ms for ν ≥ 1 and 125 ms for ν ≥ 2, are indeed about twice as large as the theoretical lifetimes for ν = 1 and ν = 2, respectively, indicating that the large experimental lifetimes may be accounted for by radiative cascade from the upper vibrational levels.     

Lifetimes of the vibronic Ã2A1 states of H2O+ and of the 3Πi (υ′ = 0) state of OH+

Using the delayed coincidence technique, lifetimes have been measured for some Σ and Π vibronic òA₁ states of H₂O⁺ and for the ³Π_i (υ′ = 0) state of OH⁺ by analysing the decay curves of the òA₁(0, υ′₂, 0) ? X?²B₁ (0, υ″₂, 0) and the ³Π_i(υ′ = 0) ? ³Σ^?(υ″ = 0) emission intensities respectively. The excited molecular ionic states are produced via excitation of H₂O molecules by 200 eV electrons. For H₂O⁺(òA₁) the vibronic Σ levels with υ′₂ = 13 and 15 and the vibronic Π levels with υ′₂ = 12 and 14 have been considered. The radiative lifetimes obtained for these levels have about the same value, namely 10.5(±1) × 10^?6 s. The radiative lifetime for the OH⁺(³Π_iυ′= 0) state is 2.5(±0.3) × 10^?6 s. The lifetimes found in this work for H₂O⁺(òA₁) and OH⁺(³Π_i,υ′= 0) are about ten and three times longer respectively than the corresponding lifetimes given by other investigators [1,2]. The probable reason for this discrepancy is that in the other experiments no attention has been paid to the presence of a large space charge effect. This effect is caused by the positive ions which are created by the primary electron beam.     

Ab initio transition probabilities,band strengths and lifetimes for the lowest-lying vibrational states of Li+3

By calculating the dipole moments at 65 discrete points on a dipole moment hypersurface and by fitting a power series analytical function to these points, we have determined the ab initio transition probabilities, band strengths and lifetimes for the ten lowest-lying states of ⁷Li⁺₃ (⁶Li⁺₃). Of these, the fourth and tenth states were found to have long lifetimes of the order 4907 s(3344 s) and 1648 s(1093 s) respectively which is in accordance with the fact that transitions from these states to the ground state are dipole forbidden.