Spectroscopic Constants Research Articles

High-resolution laser spectroscopy of the [formula omitted]1[formula omitted] – [formula omitted]1[formula omitted] transition of 13C12C12C and 12C13C12C

We present a laser spectroscopic study of the Ã1Πu – X̃1Σg+ transition of 13C mono-substituted C3 in the 378–406 nm region. The 13C12C12C and 12C13C12C isotopologues are produced in a pulsed jet expansion, by DC discharging a gas mixture of ∼0.3% C2H2/Ar (with ∼1% 13C natural abundance). By using laser induced fluorescence spectroscopy, thirteen vibronic bands belonging to the Ã1Πu – X̃1Σg+ electronic transition have been recorded for 13C12C12C and 12C13C12C, eleven of which have not been reported before. The transitions cover the three fundamental vibrational modes (ν1,ν2l,ν3). For all the vibronic bands, the full width at half maximum of spectral lines is found to be narrower than 0.023 cm-1, allowing to determine the transition frequencies with an absolute accuracy of ∼0.003 cm-1. Moreover, rotational analyses of the high-resolution data have yielded accurate spectroscopic constants for the upper vibronic states studied here. The 100–000, 04+0–000 and 12−0–000 bands of 13C12C12C, and the 02+0–000 and 04−0–000 bands of 12C13C12C are found to be less blended by spectral features of 12C3, and thus may be used for astronomical searches of 13C12C12C and 12C13C12C in the space.

Coupled-cluster method for the electronic structure and spectroscopic constants in halohydride cations with spin–orbit coupling

Spin-orbit coupling (SOC) effects in equilibrium geometries, electron affinities and adiabatic excitation energies of the low-lying states for a series of halohydride cations are reported with the equation-of-motion coupled-cluster method (EOM-SOC-CC) using relativistic effective core potentials. An approximation of this method, called EOM-SOC-CC-a, is introduced in order to reduce the computational effort for ionization potentials (IPs) without sacrificing accuracy significantly. SOC is increasingly important for the heavier halohydride cations and their calculated properties are well described by the EOM-SOC-CC method. As a cheap method, EOM-SOC-CC-a is recommended with satisfactory accuracy for the calculation of IPs up to the fifth row and the electronic structure up to the fourth row.

The fundamental rotational transition of NO+

The pure rotational spectrum of the 14NO+ cation has been revisited and its fundamental transition measured for the first time. Using a cryogenic ion trap apparatus and applying an action spectroscopy scheme, the transitions J′←J″=1←0 through J′←J″=3←2 have been detected, exhibiting well-resolved hyperfine structure from the presence of the 14N nucleus. Compared to former investigations, the spectroscopic constants are considerably improved and the nuclear spin - rotation interaction constant determined for the first time.

Ab initio investigation of ground and excited states of ScH molecule

The theoretical study of the electronic structure of Scandium Hydride ScH has been carried out using ab-initio methods. By employing (MRCI-SD/SA-CASSCF) and by using basis sets involving contribution of all electrons of both Scandium and Hydrogen atoms, 18 singlet and 15 triplet low-lying electronic states have been calculated below 28803 cm−1. Potential energy curves have been plotted and the term values at equilibrium Te, the vibrational constants ωe and ωeχe of ScH electronic states have been fitted. In addition, we calculated the permanent electric dipole moments for all these predicted states, the transition dipole moments TDMs within states at a range of internuclear distance around the equilibrium, the vibronic intensities FCF and the radiative lifetime. The calculated spectroscopic constants are in excellent consistency with the available experimental results and with other previous theoretical works. These calculations also predicted many excited states unobserved experimentally. The observed perturbations in D1Π and C1Σ+ have been investigated in this work.

Frequency comb referenced spectroscopy of A-X 0-0 transitions in SH.

We report absolute transition frequencies for the allowed transitions from the X2Π3/2, v″ = 0, J″ = 3/2 rovibronic ground state of 32S1H to the A2Σ+, v' = 0 vibronic state. The frequencies have been determined with an uncertainty of less than 1 MHz, representing a more than 1000-fold improvement over previous measurements. Spectral traces are measured by scanning a frequency comb stabilized continuous-wave spectroscopy laser over the molecular transitions and detecting laser-induced fluorescence from SH molecules in a highly collimated molecular beam. To determine the absolute transition frequencies, the traces are fit with a quantum-mechanical model that accounts for saturation effects and shifts due to quantum interference. The model also provides estimates of the predissociation rate of the excited-state levels. Weighted averages of the hyperfine-resolved transition frequencies are computed in order to enable comparisons to measurements where the hyperfine structure is not resolved. These hyperfine-averaged frequencies indicate that the absolute transition frequencies determined in previous measurements were about ∼2.1 GHz (0.07 cm-1) too high. Finally, the measured transition frequencies are fit using an effective Hamiltonian model, resulting in more precise estimates of the spectroscopic constants.

Theoretical investigation of laser cooling for [formula omitted] anion by ab inito calculation

A theoretical investigation for the feasibility of laser cooling BN-anion is presented. An ab initio calculation on the three low-lying states Χ2Σ+, Α2Π and Β2Σ+ are performed at the CASSCF/MRCI + Q level. The calculated spectroscopic constants are in good agreement with the available theoretical and experimental data. Radiative properties including Franck-Condon factor, Einstein coefficients and radiative lifetimes are determined. The calculation shows that the transition B2Σ+(v')↔X2Σ+(v'') has highly diagonal FCFs, especially f00 = 0.9898, and enough short radiative lifetimes. A cooling scheme by three laser beams is proposed, which requires one main pumping laser(λ00 = 474.67 nm) and two repumping lasers (λ01 = 514.64 nm, λ12= 514.90 nm). The population dynamics of cooling is investigated with the rate equation approach. The simulation demonstrates that the population does not remain trapped within the intermediate Α2Π state. The resultant scattered photons are about2.5×104, which is expected to stop BN-anion molecule in a cryogenic beam theoretically.

Electronic structure and spectroscopy of low-lying electronic states for SH+: MRCI-F12 study including spin-orbit coupling

The explicitly correlated multireference configuration interaction method with the Davidson correction (MRCI-F12+Q) method is utilized to investigate the low-lying electronic states of SH+ with inclusion of spin-orbit coupling (SOC) effect. The potential energy curves (PECs) of 12 Λ−S states as well as those of the 25 Ω states generated from the Λ−S states under the SOC effect have been computed. The spectroscopic constants of the bound states are determined, which are in accordance with the available theoretical and experimental results. The transition dipole moments (TDMs), Franck−Condon factors (FCFs) and the radiative lifetimes of the selected transitions have been reported. At last, the SOC induced predissociation mechanisms of the A3Π state have been discussed based on our calculations.

A rotational and vibrational investigation of phenylpropiolonitrile (C6H5C3N)

The evidence for benzonitrile (C6H5CN) in the starless cloud core TMC–1 makes high-resolution studies of other aromatic nitriles and their ring-chain derivatives especially timely. One such species is phenylpropiolonitrile (3-phenyl-2-propynenitrile, C6H5C3N), whose spectroscopic characterization is reported here for the first time. The low resolution (0.5 cm−1) vibrational spectrum of C6H5C3N has been recorded at far- and mid-infrared wavelengths (50–3500 cm−1) using a Fourier Transform interferometer, allowing for the assignment of band centers of 14 fundamental vibrational bands. The pure rotational spectrum of the species has been investigated using a chirped-pulse Fourier transform microwave (FTMW) spectrometer (6– 18 GHz), a cavity enhanced FTMW instrument (6–20 GHz), and a millimeter-wave one (75–100 GHz, 141–214 GHz). Through the assignment of more than 6200 lines, accurate ground state spectroscopic constants (rotational, centrifugal distortion up to octics, and nuclear quadrupole hyperfine constants) have been derived from our measurements, with a plausible prediction of the weaker lines through calculations. Interstellar searches for this highly polar species can now be undertaken with confidence since the astronomically most interesting radio lines have either been measured or can be calculated to very high accuracy below 300 GHz.

Ab initio study of spectroscopic properties and anharmonic force fields of MNH2 (M = Li, Na, K)

The spectroscopic properties and anharmonic force fields of NaNH2 are studied in present work by DFT (B3P86 and B3PW91) and MP2 methods in combination with 6-311++G(2d, 2p) and 6-311++G(3df, 2pd) basis sets. The calculated equilibrium geometry, ground state rotational constants and centrifugal distortion constants of NaNH2 at B3P86/6-311++G(3df, 2pd) theoretical level agree very well with the corresponding experimental values. Noteworthy, some spectroscopic constants and anharmonic force fields of NaNH2, which have not been experimentally measured, are firstly predicted. In addition, the spectroscopic properties of KNH2 are also predicted at the B3P86/6-311++G(3df, 2pd) level of theory. The influences of metal atoms on the equilibrium geometry, anharmonic constants, rotational constants, centrifugal distortion constants of MNH2 (M = Li, Na, K) are analyzed intuitively. One can find that the metal atoms affect the rotational constants, part of centrifugal distortion constants (DK, DJK, HK, and HKJ), M-N bond length and some anharmonic constants of MNH2.

Highly polar molecules consisting of a copper or silver atom interacting with an alkali-metal or alkaline-earth-metal atom

We theoretically investigate the properties of highly polar diatomic molecules containing $^2S$-state transition-metal atoms. We calculate potential energy curves, permanent electric dipole moments, spectroscopic constants, and leading long-range dispersion-interaction coefficients for molecules consisting of either a Cu or Ag atom interacting with an alkali-metal (Li, Na, K, Rb, Cs, Fr) or alkaline-earth-metal (Be, Mg, Ca, Sr, Ba, Ra) atom. We use ab initio electronic structure methods, such as the coupled cluster and configuration interaction ones, with large Gaussian basis sets and small-core relativistic energy-consistent pseudopotentials. We predict that the studied molecules in the ground electronic state are strongly bound with highly polarized covalent or ionic bonds resulting in very large permanent electric dipole moments. We find that highly excited vibrational levels have maximal electric dipole moments, e.g., exceeding 13$\,$debye for CsAg and 6$\,$debye for BaAg. Results for Cu$_2$, Ag$_2$, and CuAg are also reported. The studied molecules may find application in ultracold dipolar many-body physics, controlled chemistry, or precision measurement experiments.

Electronic states of NaLi molecule: Benchmark results with Fock space coupled cluster approach.

Accurate potential energy curves (PECs) are obtained for 20 lowest lying electronic states of the NaLi molecule. The computational scheme used here is based on the multireference coupled cluster theory formulated in the (2,0) sector of the Fock space. The latter sector provides the description of states obtained by attachment of two electrons to the reference system. This makes it possible to adopt the doubly ionized NaLi+2 molecule as a Fermi vacuum. The latter has a very concrete advantage in calculations of the PECs since it dissociates into closed shell fragments (NaLi+2 → Na+ + Li+); hence, the restricted Hartree-Fock method can be used within the whole range of interatomic distances. Computed PECs and spectroscopic constants stay very close to the experimental values (if the latter are available) with the accuracy exceeding the other theoretical approaches including those based on the effective core polarization potentials. Relativistic corrections included at the infinite-order two-component level have a non-negligible effect on the accuracy of computed excitation and dissociation energies with contributions up to 50 cm-1.

Coupled Cluster Characterization of 1-, 2-, and 3-Pyrrolyl: Parameters for Vibrational and Rotational Spectroscopy.

Pyrrolyl (C4H4N) is a nitrogen-containing aromatic radical that is a derivative of pyrrole (C4H5N) and is an important intermediate in the combustion of biomass. It is also relevant for chemistry in Titan's atmosphere and may be present in the interstellar medium. The lowest-energy isomer, 1-pyrrolyl, has been involved in many experimental and theoretical studies of the N-H photodissociation of pyrrole, yet it has only been directly spectroscopically detected via electron paramagnetic resonance and through the photoelectron spectrum of the pyrrolide anion, yielding three vibrational frequencies. No direct measurements of 2- or 3-pyrrolyl have been made, and little information is known from theoretical calculations beyond their relative energies. Here, we present an ab initio quantum chemical characterization of the three pyrrolyl isomers at the CCSD(T) level of theory in their ground electronic states, with an emphasis on spectroscopic parameters relevant for vibrational and rotational spectroscopy. Equilibrium geometries were optimized at the CCSD(T)/cc-pwCVTZ level of theory, and the quadratic, cubic, and partial quartic force constants were evaluated at CCSD(T)/ANO0 for analysis using second-order vibrational perturbation theory to obtain harmonic and anharmonic vibrational frequencies. In addition, zero-point-corrected rotational constants, electronic spin-rotation tensors, and nuclear hyperfine tensors are calculated for rotational spectroscopy. Our computed structures and energies agree well with earlier density functional theory calculations, and spectroscopic parameters for 1-pyrrolyl are compared with the limited existing experimental data. Finally, we discuss strategies for detecting these radicals using rotational and vibrational spectroscopy on the basis of the calculated spectroscopic constants.

Theoretical study on the electronic structure of NaS including spin-orbit coupling

The 19 Λ-S states and the low-lying Ω states of NaS molecule are computed by using the multireference configuration method (MRCI) including spin-orbit coupling (SOC), core-valence correlation (CV), scalar relativistic effects and Davidson (+Q) correction. The potential energy curves (PECs), spectroscopic constants and dipole moments are obtained. The predissociation mechanism of A2Σ+ is investigated in detail with aid of the SOC matrix elements. Finally, the transition properties of the NaS molecule including the Franck-Condon Factors (FCFs), transition dipole moments (TDMs), and the spontaneous radiative lifetimes of lower vibrational states are investigated. Our computational results will help to understand the spectroscopic and properties for further experimental studies of NaS.

Laser cooling and electronic structure studies of CaK and its ions CaK±

Aiming at a laser cooling investigation, we have used ab initio complete active space self consistent field (CASSCF)/(MRCI +Q) calculations to study the electronic structure of the diatomic molecule CaK and its molecular ions CaK+ and CaK−. The potential energy curves and the static dipole moment curves have been investigated for the considered molecules along with the spectroscopic constants T e, ω e, B e, and R e, in addition to the values of dipole moment μ e and dissociation energy D e. Overall, 19 and 14 electronic states have been studied respectively for CaK, CaK+, from which 12 for CaK and six for CaK+ have been investigated here for the first time. Our obtained results agree well with data related to states that have been previously examined. Nineteen electronic states have been explored for CaK−, which up to our knowledge have not been previously calculated. The transition dipole moments have been calculated for the lowest Σ+–Σ+ and Σ+–Π transitions along with the Franck–Condon factor, Einstein coefficient, the spontaneous radiative lifetime, and the emission oscillator strength corresponding to the investigated transitions. A ro-vibrational analysis has been done via the canonical function approach, where the vibrational parameters E v, B v, D v, and the turning points R min and R max have been determined. These calculations showed that the molecule CaK is a suitable candidate for Doppler laser cooling, and we propose a laser cooling scheme to this end. The Doppler limit temperature T D and recoil temperature T r have values as low as T D = 51 μK and T r = 156 nK. The results should provide a useful reference for experimental spectroscopic and ultra-cold molecular physics studies.

Catalytic effect of nano cadmium phosphate catalyst on the synthesis of some (E)-3,4-dimethoxyphenylprop-2-en-1-ones

Abstract Cadmium phosphate nanomaterial was applied for the synthesis of some (E)-3,4-dimethoxyphenylprop-2-en-1-ones through microwave irradiation. Investigations made by the authors for the study of catalytic action of the nano cadmium phosphate catalyst by means of obtained yields and reusability. In this method the obtained maximum yield was 90% and the catalyst effect was not appreciably changed up to 6th time. Influence of solvents on this process was studied using normal boiling technique. Reaction in ethanol medium gave high yield than other solvents but not more than microwave method. The synthesized (E)-3,4-dimethoxyphenylprop-2-en-1-ones were analyzed through spectroscopic technique, micro analysis, yields, and physical constants. These data are confirmed by the formation of the 2-propen-1-ones.

On the relationship between spectroscopic constants of diatomic molecules: a machine learning approach.

Through a machine learning approach, we show that the equilibrium distance, harmonic vibrational frequency and binding energy of diatomic molecules are related, independently of the nature of the bond of a molecule; they depend solely on the group and period of the constituent atoms. As a result, we show that by employing the group and period of the atoms that form a molecule, the spectroscopic constants are predicted with an accuracy of <5%, whereas for the A-excited electronic state it is needed to include other atomic properties leading to an accuracy of <11%.

Theoretical Investigation on the Laser Cooling of AlD Molecule

The potential energy curves for four Λ-S and eight Ω states of the AlD molecule are calculated by using the valence internally contracted multireference configuration interaction approach with the Davidson modification (icMRCI+Q). The core-valence correlation and relativistic corrections are included. The extrapolation of potential energies to the complete basis set limit is made. Transition dipole moments (TDMs) between the six bound Ω states are also calculated by the icMRCI approach. The calculated spectroscopic constants are in good agreement with the available experimental data and theoretical values. Based on the obtained potential energy curves and transition dipole moments, highly diagonal Franck-Condon factors and vibrational branching ratios are determined for the A1π1(υ'=0,1)→X1Σ+0+(υ'') transition, short spontaneous radiative lifetime and narrow radiative width for the excited state A1π1 (υ'=0, 1) are also predicted. On this account, the optical scheme of the laser cooling for AlD molecule is constructed with A1π1(υ')↔X1Σ+0+(υ'') as the close-loop transition. The proposed laser drives X1Σ+0+(υ'')→A1π1(υ') transition by using three wavelengths (main laser beam λ00=420.96 nm; two repumping laser beams λ10=443.00 nm and λ21=448.94 nm). The Doppler temperature (TDoppler=44.94 μK) and recoiltemperature(TRecoil=3.73 μK) for the A1π1 (υ'=0)X1Σ+0+ (υ''=0) transition are also calculated. These results can provide theoretical support for the experimental study of laser-cooled AlD molecules.

Rovibrational Quantum Chemical Treatment of Inorganic and Organometallic Astrochemicals.

ConspectusOur two groups have both independently and collaboratively been pushing quantum-chemical techniques to produce highly accurate predictions of anharmonic vibrational frequencies and spectroscopic constants for molecules containing atoms outside of the typical upper p block. Methodologies employ composite approaches, relying on various levels of coupled cluster theory-most often at the singles, doubles, and perturbative triples level-and quartic force field constructions of the potential portion of the intramolecular Watson Hamiltonian. Such methods are known to perform well for organic species, and we have extended this to molecules containing atoms outside of this realm.One notable atom that has received much attention in this application is magnesium. Mg is the second-most-abundant element in the Earth's mantle, and while molecules containing this element are among the confirmed astrochemicals, its further atomic abundance in the galaxy implies that many more molecules (both purely inorganic and organometallic) containing element 12 exist in astrophysical regions in chemical sizes between those of atoms and dust-sized nanocrystals. Our approach discussed herein is producing quality benchmarks and predicting novel data for magnesium-bearing molecules.The story is similar for Al and Si, which are also notably abundant in both rocky bodies and the universe at large. While Na, Sc, and Cu may not be as abundant as Mg, Al, and Si, molecules containing Na and transition metals have also previously been reported to be detected beyond the Earth. Consequently, the need to produce spectral reference data for molecules containing such atoms is growing. While several experimental groups (including, notably, the groups in Arizona, Boston, and France/Spain) have clearly led the way in detection of inorganic/organometallic molecules in space, computational support and even rational design can provide novel avenues for the detection of molecules containing atoms not typically studied in most laboratories. The application of quantum chemistry to other elements beyond carbon and its cronies at the top right of the periodic table promises a better understanding of the observable universe. It will also provide novel and fundamental chemical insights pushing the "central science" into new molecular territory.

The high-resolution infrared analysis of the ν3 and ν6 bands of CD3Br

The ν3 parallel, and ν6 perpendicular infrared-active vibrational bands have been analyzed for both CD379Br and CD381Br at 0.0015 cm−1 resolution. The band origins for the v3 = 1 state are 577.28925(2) cm−1 and 575.97685(2) cm−1 for the CD379Br and CD381Br isotopologues, respectively; for the v6 = 1 state the band origins are 713.46997(1) cm−1 and 713.38156(1) cm−1, respectively. The v3 = 1 and v6 = 1 vibrational states are possibly the only unperturbed vibrational states in CD3Br, and thus yield the most reliable infrared spectroscopy-based determination of the ground state rotational constants. The spectroscopic constants for both vibrational states, as well as the ground vibrational state were improved compared to previous studies through a direct fit of the vibrational bands, as well as a separate fit of the ground state combination differences. Ab initio calculations were performed to examine the efficacy of high-level theoretical calculations to accurately predict spectroscopic constants. Though not used in fitting the experimental data, nuclear quadrupole hyperfine splitting by the bromine atoms was observed in both vibrational states, an uncommon observation in the infrared spectra of polyatomic molecules.

Configuration interaction study on low-lying states of AlCl molecule* *Project supported by the National Key Research and Development Program of China (Grant No. 2017YFA0403300), the National Natural Science Foundation of China (Grant Nos. 11874177, 11874179, and 11574114), the Natural Science Foundation of Jilin Province, China (Grant No. 20180101289JC), and the High Performance Computing Center of Jilin University and High Performance

High-level ab initio calculations of the Λ–S states for aluminum monoiodide (AlCl) molecule are performed by utilizing the explicitly correlated multireference configuration interaction (MRCI-F12) method. The Davidson correction and scalar relativistic correction are investigated in the calculations. Based on the calculation by the MRCI-F12 method, the spin–orbit coupling (SOC) effect is investigated with the state-interacting technique. The adiabatic potential energy curves (PECs) of the 13 Λ–S states and 24 Ω states are calculated. The spectroscopic constants of bound states are determined, which are in accordance with the results of the available experimental and theoretical studies. Finally, the transition properties of 0+(2)–X0+, 1(1)–X0+, and 1(2)–X0+ transitions are predicted, including the transition dipole moments (TDMs), Franck–Condon factors (FCFs), and the spontaneous radiative lifetimes.