This paper describes the contents of the 2016 edition of the HITRAN molecular spectroscopic compilation. The new edition replaces the previous HITRAN edition of 2012 and its updates during the intervening years. The HITRAN molecular absorption compilation is composed of five major components: the traditional line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, infrared absorption cross-sections for molecules not yet amenable to representation in a line-by-line form, collision-induced absorption data, aerosol indices of refraction, and general tables such as partition sums that apply globally to the data. The new HITRAN is greatly extended in terms of accuracy, spectral coverage, additional absorption phenomena, added line-shape formalisms, and validity. Moreover, molecules, isotopologues, and perturbing gases have been added that address the issues of atmospheres beyond the Earth. Of considerable note, experimental IR cross-sections for almost 300 additional molecules important in different areas of atmospheric science have been added to the database. The compilation can be accessed through www.hitran.org. Most of the HITRAN data have now been cast into an underlying relational database structure that offers many advantages over the long-standing sequential text-based structure. The new structure empowers the user in many ways. It enables the incorporation of an extended set of fundamental parameters per transition, sophisticated line-shape formalisms, easy user-defined output formats, and very convenient searching, filtering, and plotting of data. A powerful application programming interface making use of structured query language (SQL) features for higher-level applications of HITRAN is also provided.

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The HITRAN 2008 molecular spectroscopic database

Kraitchman has shown that a single isotopic substitution on an atom is sufficient to determine directly the coordinates of that atom with respect to the principal axes of the original molecule. Kraitchman's formulas represent exact solutions of the equations for the equilibrium moments of inertia. However, the effects of the zero‐point vibrations are such that the coordinates obtained by substitution from the ground state moments of inertia I0 are systematically less than r0. These coordinates have here been called r (substitution) or rs, and it is found that rs≃(r0+re)/2, and Is= ∑ imirsi2≃(I0+Ie)/2.In the usual method of solution, the coordinate of one atom is determined from the equation for I0, and therefore the difference I0—Is must be made up by this one coordinate. This introduces a large error in the structures normally determined from ground state constants, and results in variations of 0.01 A in structures determined from different sets of isotopic species. If instead, we obtain the structure on...

A new criterion for the determination of molecular structures from ground state rotational constants

While the attempts currently in progress in several groups for the rigorous inclusion of dispersion interactions in density functional theory (DFT) calculations mature and evolve into practical methodology, we contribute to the debate on the applicability of current functionals to the calculation of weak interaction with a systematic investigation of a few, typical, weakly bound systems. We have used both pure DFT and a hybrid approach in which the total interaction energy is partitioned into two parts: (a) the dispersion energy which, in a first approximation is the contribution due to intermonomer correlations and (b) all other interactions. The first component is accurately obtained at all distances of interest by means of a well-known damped multipolar expansion of the dispersion energy while for the second component different approximations will be evaluated. The need to avoid double counting a fraction of the correlation energy when using the hybrid approach and the choice of the appropriate functio...

Towards extending the applicability of density functional theory to weakly bound systems

The design, performance, and operation of a broadband (3–26.5 GHz) high resolution microwave spectrometer is described. In comparison to previously developed molecular beam Fabry–Perot resonator spectrometers the design presented here implements some significant improvements: a coaxially oriented beam resonator arrangement (COBRA) formed by a confocal pair of mirrors incorporating an electromechanical valve and employing two pairs of microwave antennas, and a multioctave Fourier‐transform microwave (FTMW) instrument providing the pulsed excitation source with microwave pulse phase‐inversion scheme and the low‐noise receiving system employing image‐rejection downconversion with superheterodyne as well as quadrature detection. The entire apparatus, fully automated for scanning operation, covers a frequency range of more than three octaves. The novel design of the FTMW instrument does not require any changes of the spectrometer hardware in order to reach all regions of its spectral range. While operated in h...

A multioctave coaxially oriented beam‐resonator arrangement Fourier‐transform microwave spectrometer

Figure 18 presents the C-O stretching vibrational frequencies of the first-row transition-metal monocarbonyl cations, neutrals, and anions in solid neon; similar diagrams have been reported for neutral MCO species in solid argon, but three of the early assignments have been changed by recent work and one new assignment added. The laser-ablation method produces mostly neutral atoms with a few percent cations and electrons for capture to make anions; in contrast, thermal evaporation gives only neutral species. Hence, the very recent neon matrix investigations in our laboratory provide carbonyl cations and anions for comparison to neutrals on a level playing field. Several trends are very interesting. First, for all metals, the C-O stretching frequencies follow the order cations > neutrals > anions with large diagnostic 100-200 cm-1 separations, which is consistent with the magnitude of the metal d to CO pi * donation. Second, for a given charge, there is a general increase in C-O stretching vibrational frequencies with increasing metal atomic number, which demonstrates the expected decrease in the metal to CO pi * donation with increasing metal ionization potential. Some of the structure in this plot arises from the extra stability of the filled and half-filled d shell and from the electron pairing that occurs at the middle of the TM row; the plot resembles the "double-humped" graph found for the variation in properties across a row of transition metals. For the anions, the variation with metal atom is the smallest since all of the metals can easily donate charge to the CO ligand. Third, for the early transition-metal Ti, V, and Cr families, the C-O stretching frequencies decrease when going down the family, but the reverse relationship is observed for the late transition-metal Fe, Co, and Ni families. In most of the present discussion, we have referred to neon matrix frequencies; however, the argon matrix frequencies are complementary, and useful information can be obtained from comparison of the two matrix hosts. In most cases, the neon-to-argon red shift for neutral carbonyls is from 11 to 26 cm-1, but a few (CrCO) lie outside of this range. In the case of FeCO and Fe(CO)2, it appears that neon and argon trap different low-lying electronic states. In general, the carbonyl neutrals and anions have similar shifts but carbonyl cations have larger matrix shifts. For example, the FeCO+ fundamental is at 2123.0 cm-1 in neon and 2081.5 cm-1 in argon, a 42.5 cm-1 shift, which is larger than those found for FeCO- (11.7 cm-1) and FeCO (11.7 cm-1). It is unusual for different low-lying electronic states to be trapped in different matrices, but CUO provides another example. The linear singlet state (1047.3, 872.2 cm-1) is trapped in solid neon, and a calculated 1.2 kcal/mol higher triplet state is trapped in solid argon (852.5, 804.3 cm-1) and stabilized by a specific interaction with argon. The bonding trends are well described by theoretical calculations of vibrational frequencies. Table 5 compares the scale factors (observed neon matrix/calculated) for the C-O stretching modes of the monocarbonyl cations, neutrals, and anions of the first-row transition metals observed in a neon matrix using the B3LYP and BP86 density functionals. Most of the calculated carbonyl harmonic stretching frequencies are within 1% of the experimental fundamentals at the BP86 level of theory, while calculations using the B3LYP functional give frequencies that are 3-4% higher as expected for these density functionals and calculations on saturated TM-carbonyls. For second- and third-row carbonyls using the BP86 density functional and the LANL effective core potential in conjunction with the DZ basis set, the agreement between theory and experiment is just as good. For example, the 16 M(CO)1-4 neutral and anion and 2 MCO+ cation (M = Ru, Os) carbonyl frequencies are fit within 1.5%. The 16 species (M = Rh, Ir) are fit within 1%, but the Rh(CO)1-4+ calculations are 2-3% too low and Ir(CO)1-4+ computations are 1-2% too low. In addition to predicting the vibrational frequencies, DFT can be used to calculate different isotopic frequencies, and isotopic frequency ratios can be computed as a measure of the normal vibrational mode in the molecule for an additional diagnostic. For diatomic CO, the 12CO/13CO ratio 1.0225 and C16O/C18O ratio 1.0244 characterize a pure C-O stretching mode. In a series of molecules such as RhCO+, RhCO, and RhCO-, where the metal-CO bonding varies, the Rh-C, C-O vibrational interaction is different and the unique isotopic ratios for the carbonyl vibration are characteristic of that particular molecule. Table 6 summarizes the isotopic ratios observed and calculated for the RhCO+,0,- species. Note that RhCO+ exhibits slightly more carbon-13 and less oxygen-18 involvement in the C-O vibration than CO itself and that this trend increases to RhCO and to RhCO- as the Rh-C bond becomes shorter and stronger. Note also how closely the calculated and observed ratios both follow this trend. In a molecule with two C-O stretching modes, for example, bent Ni(CO)2 exhibits a strong b2 mode at 1978.9 cm-1 and a weak a1 mode at 2089.7 cm-1 in solid neon, and these two modes involve different C and O participations. The symmetric mode shows substantially more C (1.0242) and less O (1.0217) participation than does the antisymmetric mode with C (1.0228) and O (1.0238) involvement, based on the given isotopic frequency ratios, which are nicely matched by DFT calculations (a1 1.0244, 1.0224 and b2 1.0232, 1.0241, respectively). These investigations of vibrational frequencies in unsaturated transition-metal carbonyl cations, neutrals, and anions clearly demonstrate the value of a close working relationship between experiment and theory to identify and characterize new molecular species.

Spectroscopic and theoretical investigations of vibrational frequencies in binary unsaturated transition-metal carbonyl cations, neutrals, and anions.

The tunneling-rotation transitions of malonaldehyde, 43 a-type Q-branch lines, were observed in the submillimeter-wave region of 643–651 GHz. The proton tunneling splitting in the ground state, ΔE0=647 046.208±0.019 MHz, and the interaction constant, F=45.8965±0.0082 MHz, were determined, as well as the molecular constants for each tunneling sublevel.

Detection of the tunneling-rotation transitions of malonaldehyde in the submillimeter-wave region

Rotational spectra of tropolone in the ground vibronic state were measured by microwave spectroscopy. Due to the proton tunneling motion, the ground state is split into a doublet, of which the lower and upper components are denoted by 0+ and 0−, respectively. In the frequency region 28–84 GHz, more than 150 pure rotational transitions obeying a-type selection rules were observed for each of the 0+ and 0− states. Additionally, tunneling-rotation transitions connecting the lower (0+) and upper (0−) components of the tunneling doublet were observed by pulsed Fourier transform microwave spectroscopy. Twenty-three P- and Q-branch lines were observed in the frequency region of 10–18 GHz, and analyzed combined with the pure rotational transitions for each of the 0+ and 0− states. The proton tunneling splitting in the ground state, Δ0=29 193.788±0.026 MHz, and the tunneling-rotation interaction constant F=16.456±0.015 MHz, were determined, as well as the rotational and centrifugal distortion constants. The dipole moment along the a axis, responsible for the rotational transitions, was determined to be 3.428±0.050 and 3.438±0.050 D for the 0+ and 0− states, respectively.

Determination of the proton tunneling splitting of tropolone in the ground state by microwave spectroscopy

Laser–microwave double resonance (LMDR) with high electric field was applied to the OCS molecule. Stark Lamb‐dip spectra due to the infrared transitions of the 2ν2(0200–0000, 9.6 μm), 2ν1 (2000–0000, 5.8 μm), and ν1+2ν2 (1200–0000, 5.3 μm) bands were observed with the CO2 and CO lasers. The spectra due to the corresponding hot bands; 0310–0110, 0400–0200, 1200–1000, 1310–1110; 2110–0110, 3000–1000; 1400–0200, 1420–0220, 1510–0310, 2200–1000; and a few bands of OC34S and O13CS were also identified. Associated with these infrared transitions, more than 90 LMDR signals were detected and assigned to rotational transitions in the 11 vibrational states 0000, 1000, 2000, 0110, 0200, 0220, 0310, 0400, 1200, 1420, and 2200 of the normal species, and in the two vibrational states 0000 and 0200 of both OC34S and O13CS. Dipole moments were determined with accuracies (2.5σ) better than 2×10−5 D for all these vibrational states. Polarizability anisotropies were also obtained for some states. The data for the ground ν1 ...

CO2 and CO laser microwave double resonance spectroscopy of OCS: Precise measurement of dipole moment and polarizability anisotropy

Microwave spectrum of chlorine dioxide in excited vibrational states

The rotational spectrum of the propargyl radical (H2CCCH) was recorded with Fourier-trans-form microwave (FTMW) spectrometer coupled with a pulsed discharge nozzle (PDN). Fine and hyperfine components belonging to the 101−000, 202−101, 212−111, and 211−101 rota-tional transitions in the 2B1 ground vibronic state were observed. The analysis of the FTMW spectra resulted in the following ground-state molecular constants, with 3σ uncertainties given in parentheses. The rotational and centrifugal distortion constants are B0=9523.6775(60) MHz, C0=9206.8805(60) MHz, ΔN=3.44(63) kHz, and ΔNK=0.3753(28) MHz. The spin–rotation coupling constants are eaa=−529.386(60), ebb=−11.524(30), and ecc=−0.520(32) MHz. The hyperfine coupling constants are aF=−36.323(24), Taa=17.400(24), and Tbb=−17.220(37) MHz for the acetylenic (CH) proton, and aF=−54.21(11) and Taa=−14.121(19) MHz for the methylenic (CH2) proton. The derived hyperfine coupling constants indicate compar-able contributions of the allenyl (H2C=C=CH) and proparg...

Keiichi Tanaka

Papers

Detection of the tunneling-rotation transitions of malonaldehyde in the submillimeter-wave region

Determination of the proton tunneling splitting of tropolone in the ground state by microwave spectroscopy

CO2 and CO laser microwave double resonance spectroscopy of OCS: Precise measurement of dipole moment and polarizability anisotropy

Microwave spectrum of chlorine dioxide in excited vibrational states

Pulsed discharge nozzle Fourier transform microwave spectroscopy of the propargyl radical (H2CCCH)