In the excited vibronic states of naphthalene, there exist various interesting interactions such as intramolecular vibrational energy redistribution (IVR), intersystem crossing (ISC), and internal conversion (IC). More than thirty yeas ago, Beck et al. showed that IVR became remarkable when the excess energy exceeded about 2000 cm^{−1, a}. In the present study, we observe Doppler-free two-photon absorption spectra of A¹B_1u ← X¹A_g 8¹₀4¹₀ band of naphthalene around 34281 cm⁻¹. The excess energy is 2261 cm⁻¹, which is just above the threshold of IVR. Thus we expect this band is suitable to analyze the dynamics in the excited vibronic states. In our experiment, the spectral resolution is about 100 kHz, and rovibronic lines are well-resolved. To decide the transition frequencies, frequency shifts, and spectral linewidths with high accuracy and precision, we employed the comb-referenced Doppler-free two-photon absorption spectroscopic system^b. We proceed to assign the rovibronic lines in ^qQ transition, and to determine molecular constants in the excited vibronic state. ^a S. M. Beck, J. B. Hopkins, D. E. Powers, and R. E. Smalley, J. Chem. Phys. 74, 43(1981). ^b A. Nishiyama, K. Nakashima, A. Matsuba, and M. Misono, J. Mol. Spectrosc. 318, 40 (2015).

r0pt Figure In the present study the ground state as well as the lowest ⁴Σ⁺ state were determined for 16 AK-AKE molecules. J. V. Pototschnig, A. W. Hauser and W. E. Ernst, Phys. Chem. Chem. Phys., 2016,18, 5964-5973ultireference configuration interaction calculations were carried out in order to understand the bonding of diatomic alkali-alkaline earth (AK-AKE) molecules. The correlations between molecular properties (disociation energy, bond distances, electric dipole moment) and atomic properties (electronegativity, polarizability) will be discussed. A correlation between the dissociation energy and the dipole moment of the lowest ⁴Σ⁺ state was observed, while the dipole moment of the lowest ²Σ⁺ state does not show such a simple dependency. In this case an empirical relation could be established. The class of AK-AKE molecules was selected for this investigation due to their possible applications in ultracold molecular physics.

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J. V. Pototschnig, A. W. Hauser and W. E. Ernst, Phys. Chem. Chem. Phys., 2016,18, 5964-5973M

A canonical approach is used to investigate prototypical multi-dimensional intermolecular interaction potentials characteristic of categories in van der Waals, hydrogen-bonded, and halogen-bonded intermolecular potential energy functions. It is demonstrated that well-characterized potentials in Ar-HI, OC-HI, OC-HF, and OC-BrCl, can be canonically transformed to a common dimensionless potential with relative error less than 0.010. The results indicate common intrinsic bonding properties despite other varied characteristics in the systems investigated. The results of these studies are discussed in the context of the previous statement made by J. C. Slater [J. Chem. Phys. 57 (1972) 2389] concerning fundamental bonding properties in the categories of interatomic interactions analyzed.

A previously-unobserved emission continuum, peaking at  ∼  380 nm, has been observed when Hg vapor is photoexcited at 248 nm (KrF laser). Attributed to the mercury trimer, Hg₃, this emission continuum has a spectral breadth (FWHM) increased from  ∼  65 to  ∼  90 nm and a decay rate growed from  ∼ 6 ×10³ to  ∼ 7 ×10³ second⁻¹, corresponding to Hg vapor density rising from  ∼ 10¹⁶ to  ∼ 2 ×10¹⁹ cm⁻³. Comparisons of the observed spectra with theory Kitamura, Hikaru. "Theoretical potential energy surfaces for excited mercury trimers." Chemical physics 325.2 (2006): 207-219.uggest that continuum arises from transitions of the molecule of D_∞h symmetrical linear, D_3h equilateral triangular and C_2h equilateral triangular configurations. Kitamura, Hikaru. "Theoretical potential energy surfaces for excited mercury trimers." Chemical physics 325.2 (2006): 207-219.s

Velocity Modulation Spectroscopy (VMS) has stood as the gold standard in molecular ion spectroscopy for 30 years. Whether in a traditional uni-directional experiment or more complicated cavity-enhanced layouts with additional layers of modulation, VMS remains the preferred ion detection scheme and is responsible for the detection and transition frequency determination of around 50 molecules. Despite its success, VMS still has a great deal of untapped potential. There have only been two other published studiesH. Gao et al., Acta Phys. Sin. 50, 1463 (2001).S. Civis, Chem. Phys. 186, 63 (1994). of VMS lineshapes and both struggle with the highly correlated parameters: linewidth, intensity, and velocity modulation amplitude, i.e. the maximum Doppler shift during a period of the discharge. Due to this difficulty, both Gao and Civis made concessions to achieve a good fit. Careful analysis of the contour of the transition profile allows us to properly disentangle those parameters in order to probe the environment of the positive column. We can extract the precise values for the translational temperature of the ion, the relative transition intensity, the ion mobility, and the electric field strength just from the lineshape of a single transition. A firm understanding of the lineshape will facilitate chemical and physical investigations of positive columns and allow for a better understanding of more complicated detection schemes.

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H. Gao et al., Acta Phys. Sin. 50, 1463 (2001).

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Noise Immune Cavity Enhanced Optical Heterodyne Velocity Modulation Spectroscopy (NICE-OHVMS) is a successful technique that we have developed to sensitively, precisely, and accurately record transitions of molecular ions.K.N. Crabtree et al., Chem. Phys. Lett. 551, 1 (2012).t has been used exclusively as a method for precise transition frequency measurement via saturation and fitting of the resultant Lamb dips. NICE-OHVMS has been employed to improve the uncertainties on H₃⁺, CH₅⁺, HeH⁺, and OH⁺, reducing the transition frequency uncertainties by two orders of magnitude.J.N. Hodges et al., J. Chem. Phys. 139, 164201 (2013).A.J. Perry et al., J. Mol. Spectrosc. 317, 71 (2015).A.J. Perry et al., J. Chem. Phys. 141, 101101 (2014).C.R. Marcus et al., Astrophys. J. 817, 138 (2016). Because NICE-OHVMS is a saturation technique, this provides a unique opportunity to access information about the ratio of the transition dipole moment to the relaxation rate of the transition. This can be done in two ways, either through comparison of Lamb dip depth to the transition profile or comparison of the absorption intensity and dispersion intensity. Due to the complexity of the modulation scheme, there are many parameters that affect the apparent intensity of the recorded lineshape. A complete understanding of the lineshape is required to make the measurements of interest. Here we present a model that accounts for the heterodyne modulation and velocity modulation, assuming that the fundamental lineshape is represented by a Voigt profile. Fits to data are made and interpreted in order to extract the saturation parameter. K.N. Crabtree et al., Chem. Phys. Lett. 551, 1 (2012).I J.N. Hodges et al., J. Chem. Phys. 139, 164201 (2013).

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A.J. Perry et al., J. Chem. Phys. 141, 101101 (2014).

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Ultrafast electron diffraction experimental data for the structural parameters of molecules in excited electronic states are comparatively uncommon, hence these parameters are largely unknown. However, because differences between the molecular geometries of excited and ground electronic states cause differences in their experimental vibrational spectra it is important to establish a correspondence between the molecular vibrational frequencies in the ground state and those of the excited state of interest. The correct co-assignment of the experimental vibrational frequencies between two different electronic states of a molecule may be determined by the analog of the Duschinsky matrixF. Duschinsky, Acta Physicochim. URSS, 7(4), 551-566 (1937).D. This matrix D is defined as D = (L_I)^–1L_II where L_I and L_II are the matrices of the vibrational modes of the two states of the molecule under investigation. They are obtained by solving the vibrational problems in the I and II electronic states, respectively. Choosing the dominant elements in columns of the D matrix and permuting these columns to arrange these elements along the diagonal of the transformed matrix D^ makes it possible to establish the correct co−assignment of the calculated frequencies in the two electronic states. The rows of D^ are for the vibrations in the I electronic state, whereas the columns are for vibrations in the II electronic state. The results obtained may be tested by analogous calculations of D^ for isotopologues. The feasibility of co−assignments of the vibrational frequencies in the ground and T_1 and S_1 excited electronic states are demonstrated for trans−C_2O_2F_2Yu. N. Panchenko, Vibrational spectroscopy, 68, 236-240 (2013). The analogs of the Duschinsky matrix D^ were used to juxtapose the vibrational frequencies of this molecule calculated at the CASPT2/cc−pVTZ level in the S_0, T_1 and S_1 Yu.N.Panchenko, Vibrational spectroscopy, 68, 236240 (2013)..

A Doppler broadening thermometry (DBT) instrument is implemented based on a laser-locked cavity ring-down spectrometer. [1,2] It can be used to determine the Boltzmann constant by measuring the Doppler width of a molecular ro-vibrational transition in the near infrared. Compared with conventional direct absorption methods, the high-sensitivity of CRDS allows to reach satisfied precision at lower sample pressures, which reduces the influence due to collisions. By measuring the ro-vibrational transition of C₂H₂ at 787 nm, we demonstrate a statistical uncertainty of 6 ppm (part per million) in the determined linewidth by several hours' measurement at a sample pressure of 1.5 Pa. [3] However, the complicity in the spectrum of a polyatomic molecule induces potential systematic influence on the line profile due to nearby "hidden" lines from weak bands or minor isotopologues. Recently, the instrument has been upgraded in both sensitivity and frequency accuracy. A narrow-band fiber laser frequency-locked to a frequency comb is applied, and overtone transitions at 1.56 μm of the ¹²C¹⁶O molecule are used in the CRDS-DBT measurements. The simplicity of the spectrum of the diatomic CO molecule eliminates the potential influence from "hidden" lines. Our preliminary measurements and analysis show that it is feasible to pursue a DBT measurement toward the 1 ppm precision.

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H. Pan, et al., Rev. Sci. Instrum. 82, 103110 (2011)

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Y. R. Sun, et al., Opt. Expr., 19, 19993 (2011)

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C.-F. Cheng, et al., Metrologia, 52, S385 (2015)

l0pt Figure We have synthesized 1-aza-adamantane-4-one (C₉H₁₃NO) starting from commercial 1,4-cyclohexanedionemonoethylene acetal and tosylmethylisocianide and following a procedure described in details in the literature.Black, R. M. Synthesis, 1981, 829he high degree of sample purity was demonstrated by gas chromatography and mass spectrometric measurements, and its structure evidenced by 1H and 13C NMR spectroscopy. We present a thorough spectroscopic characterization of this molecule by gas phase vibrational and rotational spectroscopy. Accurate vibrational frequencies have been determined by infrared and far-infrared spectra. The pure rotational spectrum of the molecule has been recorded both by cavity-based Fourier-transform microwave spectroscopy in the 2-20 GHz region, by supersonically expanding the vapor pressure of the warm sample, and by room-temperature absorption spectroscopy in the 140-220 GHz range. Quantum-chemical calculations have enabled a fast analysis of the spectra. Accurate sets of rotational and centrifugal distorsion parameters of 1-aza-adamantane-4-one in its ground state and five vibrationally excited states have been derived from these measurements.

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Black, R. M. Synthesis, 1981, 829T

We recently began an investigation into the perfluoropropionic acid…formic acid complex using broadband microwave spectroscopy. This study aims to examine the possible double proton transfer between the two interacting carboxcyclic acid groups. The spectrum presented as a doubled set of lines, with spacing between transitions of <  1  MHz. Transitions appeared to be a-type, R branch transitions for an asymmetric top. Assignment of all K_a=1,0 transitions yields decent fits to a standard rotational Hamiltonian. Treatment of the doubling as either a two state system (presumably with a double proton transfer) or as two distinct, but nearly identical conformations of the complex produce fits of similar quality. Including higher K_a transitions for the a-type, R-branch lines greatly increases the error of these fits. A previous study involving the trifluoroacetic acid…formic acid complex published observed similar high K_a transitions, but did not include them in the published fit.Martinache, L.; Kresa, W.; Wegener, M.;, Vonmont, U.; and Bauder, A. Chem. Phys. 148 (1990) 129-140.e hope to shed more light on this conundrum. Similarities to other double-well potential minimum systems will be discussed. Martinache, L.; Kresa, W.; Wegener, M.;, Vonmont, U.; and Bauder, A. Chem. Phys. 148 (1990) 129-140.W

We have demonstrated large enhancements of CH bond acidities in alcohol, ether, and amine cations through infrared predissociation spectroscopy based on the vacuum ultraviolet photoionization detection. In this study, we investigate for the cationic alkanes (pentane, hexane, and heptane) with different alkyl chain lengths. The σ electrons are ejected in the ionization of alkanes, while nonbonding electrons are ejected in ionization of alcohols, ethers, and amines. Nevertheless, the acidity enhancements of CH in these cationic alkanes have also been demonstrated by infrared spectroscopy. The correlations of their CH bond acidities with the alkyl chain lengths as well as the mechanisms of their acidity enhancements will be discussed by comparison of infrared spectra and theoretical calculations.

Broadband Terahertz-Time Domain Spectroscopy (THz-TDS) (1-10 THz) has been utilized to study the complex dielectric properties of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and 1-octanol. Previous reports on dielectric study of alcohols were limited to 5 THz. At THz (1 THz = 33.33 cm⁻¹= 4 meV) frequency range (0.1 to 15 THz), the molecular reorientation and several intermolecular vibrations (local oscillation of dipoles) may coexist and contribute to the overall liquid dynamics. We find that the Debye type relaxations barely contribute beyond 1 THz, rather three harmonic oscillators dominate the entire spectral range. To get insights on the modes responsible for the observed absorption in THz frequency range, we performed all atom molecular dynamics (MD) using OPLS force field and ab initio quantum calculations. Combined experimental and theoretical study reveal that the complex dielectric functions of alcohols have contribution from a) alkyl group oscillation within H-bonded network (  1 THz), b) intermolecular H-bond stretching (  5 THz) , and c) librational motions in alcohols. The present work, therefore, complements all previous studies on alcohols at lower frequencies and provides a clear picture on them in a broad spectral range from microwave to 10 THz.