Anharmonic Constants Research Articles

Multireference Wavefunction-Based Investigation of the Ground and Excited States of LrF and LrO.

Complete active space self-consistent field (CASSCF) and multireference configuration interaction with Davidson correction (MRCI+Q) calculations have been carried out for lawrencium fluoride (LrF) and lawrencium oxide (LrO) molecules, detailing 19 and 20 electronic states for LrF and LrO, respectively. For LrF, two dissociation channels were considered, Lr(2P)+F(2P) and Lr(2D)+F(2P). However, due to the more complex electronic manifold of LrO, three dissociation channels were computed: Lr(2P)+O(3P), Lr(2D)+O(3P), and Lr(2P)+O(1D). In addition, equilibrium bond lengths, harmonic vibrational frequencies ωe, anharmonicity constants ωeχe, ΔG1/2 values, and excitation energies Te for the ground and several excited electronic states were calculated for both molecules, for the first time. Bond dissociation energies (BDEs) were calculated for LrF and LrO using several different levels of theory: unrestricted coupled-cluster with single, double, and perturbative triple excitations (UCCSD(T)), density functional theory (B3LYP, TPSS, M06-L, and PBE), and the correlation-consistent composite approach developed for f-elements (f-ccCA).

Nuclear quantum dynamics on the ground electronic state of neutral silver dimer 107Ag109Ag probed by femtosecond NeNePo spectroscopy.

The nuclear quantum dynamics on the ground electronic state of the neutral silver dimer 107Ag109Ag are studied by femtosecond (fs) pump-probe spectroscopy using the 'negative ion - to neutral - to positive ion' (NeNePo) excitation scheme. A vibrational wave packet is prepared on the X1Σ+g state of Ag2via photodetachment of mass-selected, cryogenically cooled Ag2- using a first ultrafast pump laser pulse. The temporal evolution of the wave packet is then probed by an ultrafast probe pulse via resonant multiphoton ionization to Ag2+. Frequency analysis of the fs-NeNePo spectra obtained for a single isotopologue and pump-probe delay times up to 60 ps yields the harmonic (ωe = 192.2 cm-1), quadratic anharmonic (ωexe = 0.637 cm-1) and cubic anharmonic (ωeye = 3 × 10-4 cm-1) constants for the X1Σ+g state of neutral Ag2. The fs-NeNePo spectra obtained at different pump wavelengths provide insight into the excitation mechanism. At a pump wavelength of 510 nm instead of 1010 nm, resonant excitation of a short-lived electronically excited state of the anion followed by autodetachment results in population of higher-energy vibrational levels of the neutral ground state. In contrast, at 1140 nm dynamics with a slightly shorter beating period and different relative phase are observed. The present study demonstrates that isotopologue-specific fs-NeNePo spectroscopy provides accurate vibrational constants of mass-selected neutral clusters in their electronic ground state in the terahertz spectral region, which remains difficult to obtain directly in the frequency domain with any other type of spectroscopy of comparable sensitivity.

First-principles calculations to investigate third-order elastic constant, anharmonicity and temperature dependent second elastic constant of thermoelectric materials Cu3MSe4(M = V and Nb)

The research on material‘s mechanics is critical in thermoelectric. Herein, we study the second(Cij), third(Cijk) order elastic constants, anisotropic and pressure and temperature dependent elasticity of Cu3MSe4(M = V and Nb) utilizing density functional theory. The elasticity of Cu3MSe4(M = V and Nb) is anisotropic. In addition, the calculated Cij suggests that these materials show relatively weak mechanical properties as thermoelectric device, and the ratio of bulk modulus(B) versus shear modulus(G) suggest that they are brittle. Cijk and pressure induced Cij reveal that Cu3NbSe4 has stronger anharmonic strength than that of Cu3VSe4. Finally, the thermal expansions are evaluated via quasi-harmonic approximation, and the temperature dependent elastic constants Cij indicate that Cu3NbSe4 has weak temperature dependent than that of Cu3VSe4. This research is dedicated to the design of thermoelectric devices and discovering novel thermoelectric materials with high performance in view of mechanical properties.

Potential energy surface, quartic force fields and vibrational levels of chlorine dioxide anion

Potential energy surface was calculated for the ground electronic state of the triatomic ion ClO2− using the coupled-cluster method CCSD(T). Calculations were carried out for 1200 points on the potential energy surface, and the calculated points were fitted to the potential energy expression in terms of the internal coordinates, from which the quadratic, cubic and quartic force fields were determined. Using the second-order rovibrational perturbation theory, harmonic vibrational frequencies, anharmonicity constants and several other spectroscopic parameters were calculated, and accurate fundamental vibrational frequencies were obtained. Also, the energies of 30 lowest vibrational levels were calculated using the anharmonicity constants.

Anomalous thermal response of bulk diamond to uniaxial (100) strain: A first-principles prediction

Diamond, a material that exhibits ultrahigh thermal conductivity with a sensitive thermal response to stress, is an ideal heat-sink material in the embedded cooling paradigm. This study uses first-principles calculations with the phonon Boltzmann transport equation to predict the variation rules of the thermal conductivity of diamond along the $\ensuremath{\langle}100\ensuremath{\rangle}$ crystal direction under strains at three orders of magnitude: 0.1%, 1%, and 10.5%. Density functional theory is used to predict the stress--strain dependence of diamond and the temperature-dependent thermal conductivity of unstrained diamond. The predictions are in good agreement with the experimental results. The calculated uniaxial strain--thermal conductivity dependence results reveal that the thermal conductivity of diamond abnormally increases by approximately 15% under small-scale uniaxial strain because of the weakened anharmonic interatomic force constants. Under large-scale strain, the thermal conductivity considerably decreases because of reduced phonon group velocities and increased numbers of phonon scattering channels. The findings in this study will guide analyses of the dependence of thermal conductivity on strain in other diamondlike structures, such as Group IV element-based materials. The abnormal thermal response at small strain is expected to lead to the realization of an artificial thermal conduction channel.

Temperature Dependence of Raman Peak Shift in Single-Crystalline Si-Rich Sige

Background and Objectives Silicon-germanium (SiGe) is used for thermoelectric devices since its thermal conductivity is lower than either pure Si or Ge. Indeed, the material was used in components of the Voyager and New Horizons deep-space craft because of its superior nanoscale heat conductivity. Improving SiGe for better thermoelectric devices requires ever more precise measurements of nanoscale heat conductivity and a comprehensive study on its phonon-scattering mechanism. Especially, a relationship between Raman shift ω and temperature T (dω/dT) is required through the highly precise measurements of its temperature-dependence. Burke et al. have reported the Ge fraction dependence of dω/dT for Si-Si, Si-Ge, and Ge-Ge vibration modes of polycrystalline bulk SiGe samples with high laser power excitation [1]. However, the reported values of dω/dT may be affected by phonon scattering at grain boundaries and the local heating caused by high laser power excitation. Here, we investigated dω/dT of single-crystalline bulk SiGe and its dependence on the Ge fraction by using variable-temperature Raman spectroscopy. Experiments The (001)-oriented single-crystalline Si-rich SiGe bulk samples were prepared by two different growth methods; the Czochralski (Ge fraction: 16%) [2] and traveling liquidus zone (TLZ) methods (Ge fraction: 32 and 45%) [3]. All samples were confirmed to be strain-free by X-ray diffraction (XRD). We also measured Raman spectrum of single-crystalline Si as a reference. For Raman spectroscopy measurements, the wavelength of the excitation source was 532 nm, the focal length of the spectrometer was 2,000 mm, the laser power at the sample surface was kept to less than 1 mW. The sample temperatures were set between 50 and 300°C in 50°C steps, and the Raman signal was measured twice at each temperature (i.e., during heating and cooling). Results and Discussion Raman spectra of Si-Si mode in SiGe (Ge fraction: 16%) are shown in Fig. 1(a). With increasing temperature, the full width at half maximum (FWHM) of the Raman spectra increased and shifted toward the lower side of wavenumber. This wavenumber shift is considered to be caused by the anharmonic vibrations becoming dominant as the temperature increases, and the phonon frequency decrease due to the thermal expansion of the crystal. Figure 1(b) shows the temperature dependences of the Si-Si Raman peak shifts. We experimentally clarified the dω/dT are approximately constant in each bulk SiGe sample, as shown in Fig. 1(b). Figure 1(c) shows the Ge fraction dependence of -(dω/dT) for Si-Si mode. As a result, we found that dω/dT for Si-Si mode is independent of Ge fraction unlike the study of Burke et al. It was reported that the dω/dT depends on the coefficient of linear thermal expansion and anharmonic constants [4]. From the obtained dω/dT values in the investigated range of Ge fraction, we consider that the anharmonic constants of SiGe alloy do not change by Ge fraction. Thus, the Si-Si anharmonic vibration is supposed to be not affected by the Ge fraction in SiGe alloy. In conclusion, we determined dω/dT= -0.023 cm-1/℃ for Si-Si mode from experiments with single-crystalline bulk SiGe samples and low laser power excitation. Acknowledgement This work was supported by Grant-in-Aid for Scientific Research (21K14201).

Calculation of the anharmonic effect on the main reactions referring to ethylbenzene combustion mechanism

AbstractAbout 11 reactions related to ethylbenzene are studied in this paper using transition state theory. The YL method proposed by Yao and Lin is utilized to calculate the anharmonic and the harmonic rate constants in these reaction processes in the temperature range of 300–4,000 K, energy diagram and the temperature dependence of the rate coefficients are also presented. The calculations indicate that the harmonic rate constants are larger than the anharmonic rate constants in most cases. Especially, there is a temperature junction between the high and low relationship between the anharmonic and harmonic rate constants in several reactions. Furthermore, the calculated values are in good agreement with other theoretical ones within the allowable error. Finally, the kinetic parameters and the thermodynamic parameters are calculated. To sum up, it can be concluded that the anharmonic effect in these reactions is very significant and cannot be ignored.

Improved Geometries and Frequencies with the PFD-3B DFT Method.

Bond lengths have been calculated for a test set of 120 diatomic species, including all homonuclear diatomics, hydrides, fluorides, and oxides for elements H through Kr for which experimental data is available for comparison. The performance of the PFD-3B functional is significantly better than competitive DFT methods. The rms error in bond lengths is reduced to 0.01 Å using a moderate size 3Za1Pa + f triple-ζ basis set, with the rms error in harmonic vibrational constants, ωe, equal to 38 cm-1. A very small 2ZP0H basis set is sufficient to calculate anharmonic constants, ωeXe, within ±4 cm-1. The rotational constants, Be, agree with experiment to within ±2%, and the vibration-rotation coupling constants, αe, agree within 10%. The calculated vibrational zero-point energy, ZPE, agrees with experiment to within ±0.06 kcal mol-1 for the diatomic test set, and the error increases to just ±0.11 kcal mol-1 for a set of 12 small polyatomic species. Comparison of a detailed anharmonic analysis of the twisted ethylene cation to the PFI-ZEKE experimental data illustrates the reliability of the PFD-3B for atypical structures.

Tracking Energy Transfer across a Platinum Center.

Rigid, conjugated alkyne bridges serve as important components in various transition-metal complexes used for energy conversion, charge separation, sensing, and molecular electronics. Alkyne stretching modes have potential for modulating charge separation in donor–bridge–acceptor compounds. Understanding the rules of energy relaxation and energy transfer across the metal center in such compounds can help optimize their electron transfer switching properties. We used relaxation-assisted two-dimensional infrared spectroscopy to track energy transfer across metal centers in platinum complexes featuring a triazole-terminated alkyne ligand of two or six carbons, a perfluorophenyl ligand, and two tri(p-tolyl)phosphine ligands. Comprehensive analyses of waiting-time dynamics for numerous cross and diagonal peaks were performed, focusing on coherent oscillation, energy transfer, and cooling parameters. These observables augmented with density functional theory computations of vibrational frequencies and anharmonic force constants enabled identification of different functional groups of the compounds. Computations of vibrational relaxation pathways and mode couplings were performed, and two regimes of intramolecular energy redistribution are described. One involves energy transfer between ligands via high-frequency modes; the transfer is efficient only if the modes involved are delocalized over both ligands. The energy transport pathways between the ligands are identified. Another regime involves redistribution via low-frequency delocalized modes, which does not lead to interligand energy transport.

Spectroscopic and quantum mechanical study of a scavenger molecule: N,N-diethylhydroxylamine

We report a combination of quantum mechanical calculations and a range of spectroscopic measurements in the gas phase of N,N-diethylhydroxylamine, an important scavenger compound. Three conformers were observed by pulsed jet Fourier transform microwave spectroscopy in the 6.5–18.5 GHz frequency range. They are characterized by the hydroxyl hydrogen atom being in trans orientation with respect to the bisector of the CNC angle while the side alkyl chains can be both trans (global minimum, Cs symmetry, A = 7608.1078(4), B = 2020.2988(2) and C = 1760.5423(2) MHz) or one trans and the other gauche (second energy minimum, A = 5302.896(1), B = 2395.9822(4) and C = 1804.8567(3) MHz) or gauche’ (third energy minimum, A = 5960.8025(6), B = 2273.6627(4) and C = 1975.8074(4) MHz). For the global minimum, the 13Cα,13Cβ and 15N isotopologues were observed in natural abundance, allowing for an accurate partial structure determination. Moreover, several lines were detected by free jet absorption millimeter wave spectroscopy in the 59.6–74.4 GHz spectral range. The electron binding energies of the highest occupied molecular orbital and the next-to-highest occupied molecular orbital, determined by photoelectron spectroscopy, are 8.95 and 10.76 eV, respectively. Supporting calculations evidence that, (i) upon ionization of the HOMO, the molecular structure changes from an amine to an N-oxoammonium arrangement and (ii) the 0–0 of the HOMO-1 photoionization is 10.46 eV. The K-shell binding energies, determined by X-ray photoelectron spectroscopy, are 290.42 eV (Cβ), 291.45 eV (Cα), 405.98 eV (N) and 538.75 eV (O). The Fourier transform near infrared spectrum is reported and a tentative assignment is proposed. The equilibrium wavenumber (ω̃ = 3811 cm−1) and the anharmonicity constant (ω̃χ = −87.5 cm−1) of the hydroxyl stretching mode were estimated using a quadratic model.

Laser-induced fluorescence spectroscopy of the B 5Π-1 – X 5Π-1 system of the chromium monosulfide molecule

Laser induced fluorescence and dispersed fluorescence spectroscopy was used to investigate the B 5Π-1 – X 5Π-1 system of the chromium monosulfide molecule. The rotational constant and Λ-doubling parameter of B 5Π-1 (v′ = 7), as a newly observed upper vibrational level, were obtained from the rotationally resolved laser excitation spectrum. For the ground X 5Π-1 state, the vibrational frequency and vibrational anharmonicity constant were experimentally determined for the first time from the dispersed fluorescence spectrum. In addition, the lifetimes of the upper B 5Π-1 (v′ = 0 − 7) levels were measured by fitting the time-dependent fluorescence decay.

Temperature‐ and pressure‐dependent phonon dynamics properties of gallium selenide telluride

AbstractUnderstanding the thermodynamic properties of materials is a fundamental issue in physics, and its knowledge is crucial for targeting a specific material for possible applications. In this work, we report a temperature‐ and pressure‐dependent Raman study of bulk GaSe0.5Te0.5 alloy, besides their relevant thermodynamic parameters. Our results show a nonlinear redshift for the and vibrational modes as the temperature increases in the temperature range from 10 to 748 K. Such behavior is well described by considering both thermal expansion and phonon–phonon coupling contributions. By combining density functional theory (DFT) calculations and Raman spectroscopy experiments, the anharmonic constants relative to the three‐ and four‐phonon decay processes, mode‐Grüneisen parameters, Debye temperature, thermal expansion coefficient, and bulk modulus were estimated for GaSe0.5Te0.5 alloy. Furthermore, the high‐pressure measurements and DFT calculations, performed in the pressure range from 0 to 26.4 GPa, show a quadratic trend for the and modes as a function of pressure, with the modes being more compressible than one, that is, . No structural phase transition is observed until the maximum pressure reached in the experiment. This study took a step forward in the understanding of mechanical and thermal properties related to GaSe0.5Te0.5 alloy, whose determined parameters are important for designing new applications.

A computational framework for modeling and simulating vibrational mode dynamics

Atomic vibrations influence a variety of phenomena in solids and molecules, ranging from thermal transport to chemical reactions. These vibrations can be decomposed into normal modes, often known as phonons, which are collective motions of atoms vibrating at certain frequencies; this provides a rigorous basis for understanding atomic motion and its effects on material phenomena, since phonons can be detected and excited experimentally. Unfortunately, traditional theories such as the phonon gas model do not allow for the general study of vibrational modes since they only apply to ideal crystals where modes have a wave-like characteristic. Traditional computational methods based on molecular dynamics (MD) simulations allow for the study of phonons in more general systems with disorder, where the modes are less wave-like, but traditional methods do not simulate mode interactions and energy transfer between modes. Here we present, for the first time, a theory and massively parallel open-source software for modeling vibrational modes and simulating their interactions, or energy transfers, in large systems (>103 atoms) using MD. This is achieved by rewriting the atomic equations of motion in mode coordinates, from which analytical expressions for anharmonic mode coupling constants arise. Hamiltonian mechanics then provides a simple expression for calculating power transfer between modes. As a simple application of this theory, we perform MD simulations of phonon-interface scattering in a silicon–germanium superlattice and show the various pathways of energy transfer that occur. We also highlight that while many interaction pathways exist, only a tiny fraction of these pathways transfer significant amounts of energy, which is surprising. The approach allows for the prediction and simulation of mode/phonon interactions, thus unveiling the real-time dynamics of phonon behavior and energy transport.

Semiexperimental equilibrium molecular structure of phthalic anhydride

The semiexperimental equilibrium molecular structure (rese) of the title compound is derived from the experimental rotational constants of the parent molecule and a number of isotopologues using a quantum-chemical force field. The quadratic and cubic force fields are calculated at the B2PLYP double hybrid functional with the correlation-consistent triple-ζ cc-pVTZ basis set. The rovibrational and electronic corrections necessary for transformation of ground-state rotational constants to equilibrium ones are calculated using anharmonic (cubic) force constants and rotational g tensor, respectively. The rese structure is used to benchmark the results of coupled-cluster computations (CCSD(T)).

Infrared spectroscopy of difference and combination bands of the NO3 radical and anharmonicity analysis

The 2ν3-ν4 difference bands of 14NO3 and 15NO3 have been observed in the 1643.6 cm−1 and 1622.0 cm−1 region, respectively, and analyzed to determine molecular constants in the v3 = 2 state. The present paper also reports re-analysis of high-resolution spectra of the 15NO3 radical from 2000 to 2500 cm−1, which have been reported previously without vibrational assignments [J. Phys. Chem. A 114(2010), 980]. Three bands at 2004, 2128, and 2492 cm−1 are analyzed as the ν1 + ν3, 2ν3, and ν1 + ν3 + ν4 bands, including perturbations from nearby states. All vibrational states of 14NO3 and 15NO3 so far observed by infrared spectroscopy and laser induced fluorescence (LIF) are analyzed by using a vibrational energy matrix including cubic and quartic anhamonic effects, to determine anharmonicity constants and eigenvector coefficients. The first-order Coriolis coupling constants Cζ and the effective spin–orbit interaction constants aeff are calculated by using the eigenvector coefficients and compared with the observed values.

Conformational Gap Control in CsTaS3.

Simple arguments based on orbital energies and crystal symmetry suggest the band gap of CsTaS3 to be suitable for solar cell photovoltaics. Here, we combine chemical theory with sophisticated calculations to describe an intricate relationship between the structure and optical properties of this material. Orbital interactions govern both the presence and nature of CsTaS3's gap. In the first place, through a second-order Jahn-Teller (JT) distortion, which slides the Ta ion along the axial direction of TaS3 chains. This displacement creates a gap that remains direct in the face of minor distortions. Using an advanced methodology, compressive sensing lattice dynamics, we compute the anharmonic interatomic force constants up to the fourth order and use them to renormalize the phonons at finite temperatures. This analysis predicts CsTaS3 to undergo the JT metal-to-semiconductor transition at temperatures below 1000 K. At around room temperature, we find a second distortion that moves the Ta ion along the equatorial direction of the TaS3 chains, giving rise to many possible supercell conformations. By relaxing all symmetry-inequivalent structures with Ta ion displacements, in supercells with up to 12 formula units, we obtain 204 symmetrically distinct conformations and sort them by energy and (direct) band gap magnitude. Since all structures with a gap lie within an energy range of 30 meV/Ta above the ground state, we expect CsTaS3's optical properties to be controlled by the full polymorphic ensemble of gapped conformations. Using the GW-Bethe-Salpeter approach, we predict a band gap of 1.3-1.4 eV as well as potent absorption in the visible range.

Heavy Atom Tunneling in Organic Reactions at Coupled Cluster Potential Accuracy with a Parallel Implementation of Anharmonic Constant Calculations and Semiclassical Transition State Theory.

We describe and test on some organic reactions a parallel implementation strategy to compute anharmonic constants, which are employed in semiclassical transition state theory reaction rate calculations. Our software can interface with any quantum chemistry code capable of a single point energy estimate, and it is suitable for both minimum and transition state geometry calculations. After testing the accuracy and comparing the efficiency of our implementation against other software, we use it to estimate the semiclassical transition state theory (SCTST) rate constant of three reactions of increasing dimensionality, known as examples of heavy atom tunneling. We show how our method is improved in efficiency with respect to other existing implementations. In conclusion, our approach allows SCTST rates and heavy atom tunneling at a high level of electronic structure theory (up to CCSD(T)) to be evaluated. This work shows how crucial the possibility to perform high level ab initio rate evaluations can be.

First-Principles Calculation of Kh2po4 Anharmonic Force Constants Phonon Dispersion Curves

First-Principles Calculation of Kh2po4 Anharmonic Force Constants Phonon Dispersion Curves

Retinal Vibrations in Bacteriorhodopsin are Mechanically Harmonic but Electrically Anharmonic: Evidence From Overtone and Combination Bands.

Fundamental vibrations of the chromophore in the membrane protein bacteriorhodopsin (BR), a protonated Schiff base retinal, have been studied for decades, both by resonance Raman and by infrared (IR) difference spectroscopy. Such studies started comparing vibrational changes between the initial BR state (all-trans retinal) and the K intermediate (13-cis retinal), being later extended to the rest of intermediates. They contributed to our understanding of the proton-pumping mechanism of BR by exploiting the sensitivity of fundamental vibrational transitions of the retinal to its conformation. Here, we report on new bands in the 2,500 to 1,800 cm−1 region of the K-BR difference FT-IR spectrum. We show that the bands between 2,500 and 2,300 cm−1 originate from overtone and combination transitions from C-C stretches of the retinal. We assigned bands below 2,300 cm−1 to the combination of retinal C-C stretches with methyl rocks and with hydrogen-out-of-plane vibrations. Remarkably, experimental C-C overtone bands appeared at roughly twice the wavenumber of their fundamentals, with anharmonic mechanical constants ≤3.5 cm−1, and in some cases of ∼1 cm−1. Comparison of combination and fundamental bands indicates that most of the mechanical coupling constants are also very small. Despite the mechanical quasi-harmonicity of the C-C stretches, the area of their overtone bands was only ∼50 to ∼100 times smaller than of their fundamental bands. We concluded that electrical anharmonicity, the second mechanism giving intensity to overtone bands, must be particularly high for the retinal C-C stretches. We corroborated the assignments of negative bands in the K-BR difference FT-IR spectrum by ab initio anharmonic vibrational calculations of all-trans retinal in BR using a quantum-mechanics/molecular mechanics approach, reproducing reasonably well the small experimental anharmonic and coupling mechanical constants. Yet, and in spite accounting for both mechanical and electrical anharmonicities, the intensity of overtone C-C transitions was underestimated by a factor of 4–20, indicating room for improvement in state-of-the-art anharmonic vibrational calculations. The relatively intense overtone and combination bands of the retinal might open the possibility to detect retinal conformational changes too subtle to significantly affect fundamental transitions but leaving a footprint in overtone and combination transitions.

The eight lowest-energy vibrational states of benzonitrile: analysis of Coriolis and Darling-Dennison couplings by millimeter-wave and far-infrared spectroscopy

A combination of millimeter-wave and high-resolution infrared data is used to analyze the eight lowest-energy vibrational states of benzonitrile (C6H5CN, C2v, μa = 4.5 D), a benzene derivative recently detected in the interstellar medium. The overtone states v22 = 2 and v33 = 2, combination state v22 = 1, v33 = 1, and fundamental states v21 = 1 and v15 = 1 are studied for the first time by rotationally resolved spectroscopy. The three former states form a Coriolis- and Darling-Dennison-coupled triad of interacting states for which the coupling terms and highly precise, deperturbed energy separations have been measured. The use of sub-millimeter and far-infrared data together enabled the determination of the purely rotational and coupling parameters for the six lowest-energy vibrationally excited states of benzonitrile, along with their highly precise energies (E22 = 141.4810252 (57) cm−1, E33 = 160.5891953 (47) cm−1, E2×22 = 282.6295417 (83) cm−1, E22+33 = 302.5795909 (87) cm−1, E2×33 = 321.4923856 (77) cm−1, E21 = 372.257993 (10) cm−1). These energies, the resultant experimental anharmonicity constants (x22,22 = − 0.1663 cm−1, x33,33 = 0.1570 cm−1, and x22,33 = 0.4909 cm−1), and semi-experimental harmonic frequencies (ω22 = 142.9 cm−1 and ω33 = 161.0 cm−1) for the ν22 and ν33 states are compared to CCSD(T)/ANO1 predicted values. The spectroscopic and coupling constants determined in this work for the vibrational ground state, the two lowest-energy fundamental states, and the corresponding first overtone and combination states successfully predict experimental frequencies down to 8 GHz. Particularly for the vibrationally excited states, the ability to predict transition frequencies so far outside the frequency region in which the constants were determined confirms that the rotational and distortion constants, as well as the coupling terms, are determined reasonably close to their true values. The ability to accurately extrapolate also demonstrates the suitability of the determined constants as the basis for extraterrestrial identification and examination of these vibrational states of benzonitrile.