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Theories on the origins of life propose that early cell membranes were synthesized from amphiphilic molecules simpler than phospholipids such as fatty alcohols. The discovery in the interstellar medium (ISM) of ethanolamine, the simplest phospholipid head group, raises the question whether simple amphiphilic molecules are also synthesized in space. We investigate whether precursors of fatty alcohols are present in the ISM. For this, we have carried out a spectral survey at 7, 3, 2 and 1 mm toward the Giant Molecular Cloud G+0.693-0.027 located in the Galactic Center using the IRAM 30m and Yebes 40m telescopes. Here, we report the detection in the ISM of the primary alcohol n-propanol (in both conformers Ga-n-C3H7OH and Aa-n-C3H7OH), a precursor of fatty alcohols. The derived column densities of n-propanol are (5.5+-0.4)x10^13 cm^-2 for the Ga conformer and (3.4+-0.3)x10^13 cm^-2 for the Aa conformer, which imply molecular abundances of (4.1+-0.3)x10^-10 for Ga-n-C3H7OH and of (2.5+-0.2)x10^-10 for Aa-n-C3H7OH. We also searched for the AGa conformer of n-butanol (AGa-n-C4H9OH) without success yielding an upper limit to its abundance of, 15 pages, 10 figures, accepted for A&A

The rotational spectra of 1-butanol (1-BuOH), 1-butanethiol (1-BuSH), 2-methyl-1-propanol (iso-BuOH), and 2-methyl-1-propanethiol (iso-BuSH) were measured by Fourier transform microwave spectroscopy in the frequency region from 3.7 up to 25 GHz. The observed spectral lines were assigned by observation of the deuterium substitution effect and by ab initio or density functional theory calculations at the levels of MP2/6-311++G(d,p) or B3LYP and cam-B3LYP, respectively. For 1-BuOH and 1-BuSH, seven of the 14 conformations, anticipated to exist as stable, were detected, whereas four and three among the five possible conformations were identified for iso-BuOH and iso-BuSH, respectively. We further found that, of the seven conformers of 1-BuOH, five were trans and two gauche, with respect to the internal rotation axis: the C2-C3 bond, while three of iso-BuOH existed in gauche and one in trans. The most stable conformer of the two BuOH molecules was trans with respect to the C-O bond, while all the sulfur analogues were gauche to the C-S axis. The rare isotopomers examined included 13C and OD of 1-BuOH and OD of iso-BuOH, 34S, 13C, and SD of the two sulfur molecules, and the rotational constants obtained on these isotopomers were employed in the molecular structure derivation. The potential barrier to CH3 internal rotation and the deuterium quadrupole coupling constant, where available, were also derived from the spectral analysis, and the molecular parameters thus obtained were compared with those derived using quantum-chemical calculations; the values derived using cam-B3LYP/6-311++G(d,p) were in better agreement with the observed than those derived using MP2/6-311++G(d,p) and B3LYP/6-311++G(d,p). The TTg form of 1-BuOH and of 1-BuSH and the Tg form of iso-BuSH exhibited additional spectral splittings, which were interpreted as caused by the OH or SH group tunneling between the symmetric and antisymmetric states. Some of the J = 8 rotational levels of 1-BuSH happened to be near-degenerate with others, and the splittings in them caused by mutual repulsion could be precisely determined by the observation of the transitions involving those split levels. Such splittings were determined for 1-BuSH, 1-BuSD, and iso-BuSH to be 1694.1731 (22), 56.3174 (16), and 6.4678 (14) MHz, respectively. A natural bond orbital analysis was performed to show that the most stable conformation of the primary and secondary alcohols is Gt because of the charge transfer from the lone-pair electron of the oxygen atom to the antibonding orbital of the C-H bond in 1-BuOH, whereas in iso-BuOH, the charge transfer to the antibonding orbital of the C1-C2 bond.

We recorded the rotational spectra of N2-ethylene sulfide (ES) and N2-dimethyl sulfide (DMS) including the 15N2 and 15N14N isotopomers in the frequency range of 5-25 GHz by using a Fourier transform microwave spectrometer. The b-type transitions for the ortho and para states of 14N2-ES and 15N2-ES and c-type transitions of 14N2-DMS and 15N2-DMS were observed. The 15N14N-ES and 15N14N-DMS species were found to exist in two isomeric forms: inner (14N15N-ES and 14N15N-DMS) and outer (15N14N-ES and 15N14N-DMS). Neither the -ES nor -DMS complexes showed weak accompanying spectra, which had been observed for N2-ethylene oxide (EO). This is because the potential barriers to internal rotation of ES and DMS are higher than that of EO. The spectra were analyzed by an A-reduced asymmetric-top rotational program with less than 4 kHz standard deviation, except for the 15N14N-DMS and 14N15N-DMS complexes. Rotational, centrifugal distortion, and nuclear electric quadrupole coupling constants were determined by the spectral analysis. The V3 potential barrier to internal rotation of the two equivalent methyl groups of DMS in the ortho and para states of the 15N2-DMS complex was determined to be about 740 cm-1. We performed ab initio calculations in order to complement the information on the intracomplex motions obtained from the experimental spectra.

The unpaired electron orbital of NO3 is of a2′ symmetry in the ground electronic state, and thus its motion about the symmetry axis of the molecule is free rotation. When a degenerate vibration is excited, however, the free azimuthal rotation of the unpaired electron is perturbed much by nuclear motions of the degenerate mode, as evidenced by high-resolution spectroscopic studies. Thus the ν4 fundamental state, for example, bears some characters of the B excited electronic state through the Herzberg-Teller (H-T) interaction, and Neumark et al. explained anomalous ν4 progression in the photoelectron spectra of the NO3− anion by the H-T mechanism. However, the interaction parameter Neumark required was too large to reproduce the ν4 molecular parameters in the ground electronic state precisely determined by high-resolution IR spectroscopy. This discrepancy was resolved by the fact that the upper ν4 overtone/combination states of Neumark’s photoelectron transitions were primarily of vibrational in nature. The present study thus showed that NO3 bears both vibrational and H-T induced electronic characters in excited states of degenerate modes in the ground electronic state.

Trifluoromethylsulfur pentafluoride CF 3 SF 5 , which has been attracting much attention because of its unusually large global warming potential, was investigated by Fourier transform microwave spectroscopy in order to determine the twelve-fold potential barrier to internal rotation in this molecule. We have found the V 12 value to be close to zero. Relaxation among internal-rotation and overall-rotation levels was found inhomogeneous, resulting in distributions quite different from thermal in low-temperature molecular beam, which might affect significantly thermodynamic properties of the molecule. Rotational spectra of the 13 C species and the 34 S species were also observed in natural abundance, leading to the r s C S bond length of 1.8808 (7) A.

The ground-state rotational spectra of the whisky lactone (WL) : 5-butyl-4-methyl tetrahydrofuran-2-one were observed and analyzed by molecular beam Fourier transform microwave spectroscopy combined with quantum chemical calculations. We have detected three stereo-isomers: the trans - TTT form with a methyl CH 3 group attached to C(4) in an equatorial position ( eq ) and a butyl C 4 H 9 group to C(5) in an eq position, for which 110 b -type and 113 a -type transitions were assigned, the cis - TTT form with a CH 3 to C(4) in an axial position ( ax ) and a C 4 H 9 to C(5) in eq , for which 96 a -type, 101 b -type, and 45 c -type transitions were observed, and the cis - GTT form with a CH 3 to C(4) in ax and a C 4 H 9 to C(5) in eq , for which 158 a -type, 52 b -type, and 17 c-type transitions were observed, where TTT and GTT denote the conformations about the C(6) C(5), C(7) C(6), and C(8) C(7) bonds, with T and G designating trans and gauche , respectively. The rotational constants thus derived agree with the predictions made by quantum chemical calculations, MP2/6-311++G( d , p ) within 1.2%. The trans - TTT form was calculated to be the most stable. The splittings due to internal rotation of the terminal methyl in the butyl group were observed for all the three stereo-isomers and were analyzed by the XIAM program to determine the threefold potential barrier V 3 to be 966.4 (25), 978.8 (11), and 1098.7 (48) in cm −1 for the trans - TTT ( eq , eq ), the cis - TTT ( ax , eq ), and the cis - GTT ( ax , eq ) forms, respectively, to be compared with quantum chemically calculated values: 1055, 1055, and 1053 in cm −1 .

The double minimum potential (DMP), which Hund assumed to explain the quantum-mechanical stability of enantiomers, was discussed, by citing three typical examples of DMP: inversion, internal rotation, and puckering. They expanded the classical scope of chirality, as defined by Kelvin, and indicated that a new bridge could be formed between the three low-frequency DMP modes and the asymmetric syntheses of chiral molecules.

Rotational assignment of the high-resolution fluorescence excitation spectrum of the 14NO3 radical in the B ∼ 2E′ ← X ∼ 2A2′ transition 0–0 band region located around 15,100 cm−1 was made with the help of the ground state combination differences and the observation of Zeeman effect. We successfully identified several rotational line series based on the newly obtained rotational assignments of 162 lines with |k″| ⩽ 15 and J′ ⩽ 18.5 quantum numbers, and we estimated the effective molecular constants of the excited vibronic states.

The rotational spectra of the N2-ethylene oxide (EO) complex were measured in the frequency region from 4 to 27 GHz by Fourier transform microwave spectroscopy, paying particular attention to intracomplex motions. The isotopologues with enriched (15)N2 or (15)NN as a moiety were also investigated. We have observed spectra of a strong/weak pair for each of the ortho and para states of the (14)N2-EO and (15)N2-EO species, which indicated that the complex existed in four distinct states. We interpreted, on the basis of the observed relative intensities, that these states were generated primarily by the exchange of the nitrogen atoms of the N2 moiety, followed by that of the two CH2 groups in the EO molecule. The (15)NN-EO species was found to consist of two isomers, one with the (15)N in the inner expressed as N(15)N-EO and the other in the outer position designated as (15)NN-EO, and the spectra of both isomers were accompanied by one weak set of satellites. The observed spectra were rotationally assigned by using sum rules and were analyzed by the asymmetric-rotor program of S-reduction, with the standard deviation of less than 10 kHz. We have found some of the molecular parameters like A, D(JK), and D(K) to be correlated between the two pairs of the spectra, and also, to much less extent, between the strong and weak members. The differences in these molecular parameters between the four sets were explained by the first-order Coriolis interaction between the "ground" and "excited" states generated by a combination of the two internal motions corresponding to the exchanges of the equivalent atoms and/or groups in the N2 and EO constituents of the complex. These internal motions were simulated by the 2-fold internal rotations of the two moieties. We have carried out ab initio molecular orbital calculations at the level of MP2 with basis sets 6-311++G(d,p), aug-cc-pVDZ, and aug-cc-pVTZ, to complement the information on the intracomplex motions obtained from the observed rotational spectra.

The rotational spectra of the CO-ethylene oxide (EO), CO-ethylene sulfide (ES), CO(2)-EO, and CO(2)-ES complexes were measured by Fourier transform microwave spectroscopy in the frequency region from 4 up to 31 GHz. The isotopologues with a single (13)C atom in the EO or ES, (18)O in the EO, (34)S in the ES, and (13)C in the CO(2) moiety, respectively, were observed in natural abundance, and enriched samples, (13)CO or C(18)O in the CO-EO or CO-ES complex and C(18)OO and C(18)O(2) in the CO(2)-EO or CO(2)-ES complex, were employed to record respective rotational transitions. The rotational spectra observed for the CO-EO, CO-ES, CO(2)-EO, and CO(2)-ES complexes were analyzed by using an asymmetric-rotor S-reduced Hamiltonian to determine rotational and centrifugal distortion constants. The r(s) coordinates of the atoms in the four complexes, which were calculated from the observed rotational constants, led to a structure in which the CO or CO(2) moiety is located in a plane perpendicular to the EO or ES skeletal plane and bisecting the COC or CSC angle. We have also carried out ab initio molecular orbital calculations at the level of MP2 with basis sets 6-311++G(d,p) and aug-cc-pVDZ using the Gaussian 09 package. The MP2/6-311++G(d,p) calculations yield rotational constants in better agreement with the experimental values than with the other basis set; in other words, the molecular structures calculated using this basis set are close to those experimentally found for the ground state. The estimated dissociation energies of the complexes, including the zero-point vibrational energy corrections ΔZPV and the basis set superposition errors (BSSE) calculated with the counterpoise correction (CP), are in good agreement with the experimentally obtained binding energies E(B). We have applied an NBO analysis to the complexes to calculate the stabilization energy CT (=ΔE(σσ*)), which we found are closely correlated with the binding energies E(B). We have thus achieved a consistent overview on the intermolecular interaction in the complexes under consideration. It is to be noted that the spectral intensities of the inner OC(18)O-EO and OC(18)O-ES complexes were larger by a factor of 2 than those of the outer (18)OCO-EO/ES complexes. This observation was explained by the zero-point energy of the inner conformer being a little smaller than that of the outer one.

A new spectroscopic method of triple resonance is proposed for studying chirality of a molecule of C1 symmetry. Each enantiomer of such a molecule is of mixed parity and thus exhibits all three a-, b-, and c-types of rotational spectra. The present study concludes, by using time-dependent perturbation theory, that the transition probability between two of the three rotational levels under triple resonance differs for different enantiomer. This result can thus be of some significance for enantiomer differentiation.

The rotational spectrum of the carbon dioxide–propylene oxide (CO 2 –PO) complex was measured in the frequency region from 5 up to 24 GHz by Fourier transform microwave spectroscopy. For the normal species 82 a -type, 53 b -type, and 43 c -type transitions were observed, while a -type and b -type transitions were assigned for the four isotopic species with one 13 C in each of the PO or CO 2 moiety in natural abundance. Enriched C 18 OO and C 18 O 2 samples were employed to record a -type, b -type, and c -type transitions for the complexes with the respective isotopic CO 2 species bound to PO, including the two different C 18 OO–PO complexes: the inner OC 18 O–PO and the outer 18 OCO–PO. All the observed transition frequencies were analyzed for the normal and the three 18 O–carbon dioxide complexes using a one CH 3 group internal rotation and overall rotation Hamiltonian. The potential barrier height V 3 to internal rotation of the CH 3 in the PO was determined to be 859.8 (62) cm −1 . The rotational constants derived for the CO 2 –PO complex led to the structure in which the CO 2 moiety was located in one side of the PO ether plane opposite to that of the CH 3 group, namely an anti -conformer. The intermolecular bonding of the CO 2 –PO was found weaker than those of the CO 2 –EO and the CO 2 –DME; by assuming a Lennard–Jones-type potential, the force constant of the van der Waals stretching mode and the dissociation energy were estimated to be 5.0 N m −1 and 5.7 kJ mol −1 , respectively, which were to be compared with those of the CO 2 –EO and the CO 2 –DME: 8.0 N m −1 and 7.1 kJ mol −1 and 10.9 N m −1 and 9.7 kJ mol −1 , respectively. It is interesting to note that the intensities of the inner OC 18 O–PO spectra are stronger than those of the outer 18 OCO–PO ones. This observation was explained by the zero-point energy of the inner conformer being a little smaller than that of the outer.

The rotational spectrum of the CO–dimethyl sulfide (DMS) complex was measured in the frequency region from 4.8 up to 25 GHz by Fourier transform microwave spectroscopy. For the normal species 27 a -type and 57 c -type transitions were observed, while 16 and 8 c -type transitions were assigned for the species with 34 S and 13 C in the DMS moiety, respectively, in natural abundance. In addition, 7 a -type and 48 c -type transitions were assigned for the complex with the 13 CO enriched species as a component and 9 a -type and 42 c -type transitions for the complex with enriched C 18 O. No splitting was observed, which could be ascribed to the tunneling motion of the CO between two possible potential minima around DMS, while many transitions were split by the internal-rotation of the two methyl tops of the DMS unit. In cases where the K -type splitting was close to the methyl internal-rotation splitting, forbidden transitions were observed which apparently followed b -type selection rules. All of the observed transition frequencies for the normal species were analyzed simultaneously using a two-top internal-rotation and rotation Hamiltonian. The potential barrier height V 3 to internal rotation of the methyl groups of the DMS was determined to be 745.5 (30) cm −1 . The transition frequencies observed for all the isotopomers were analyzed using an asymmetric-rotor rotational Hamiltonian, to determine rotational and centrifugal distortion constants. The r s coordinates calculated from the observed rotational constants led to the conclusion that the CO moiety was located in a plane perpendicular to the skeletal plane of the DMS and bisecting its CSC angle. This structure of the CO–DMS is very much different from that of the CO–DME, in which the CO is located in the DME skeletal plane. The distance between the centers of gravity of the two moieties, R cm , was calculated to be 3.789 A for the CO–DMS, which is longer by only 0.11 A than that in the CO–DME complex: 3.68 A, in spite of the fact that the van der Waals radius of the S atom is much larger than that of the O atom. The small difference in R cm is, in part, ascribed to the location of the CO relative to the DMS/DME. The more important reason is that the intermolecular bonding of the CO–DMS is stronger than that of CO–DME; by assuming a Lennard–Jones-type potential, the force constant of the van der Waals stretching mode and the dissociation energy were estimated to be 2.7 Nm −1 and 3.3 kJ mol −1 , respectively, which were larger than those of the CO–DME: 1.4 Nm −1 and 1.6 kJ mol −1 .

Rotational spectra of both trans and cis forms of the N-methylformamide normal as well as deuterated (HCONDCH3, referred to as N–D) species were observed by Fourier transform microwave spectroscopy in the frequency region from 5 to 118 GHz. Samples were prepared in the form of a beam by a pulsed jet valve maintained at 50 °C and were introduced in a high-vacuum cavity cell, with either Ne or Ar as a carrier gas at a backing pressure of 100 kPa. The observed spectra were analyzed to yield molecular parameters including rotational constants and barrier, V3, to CH3 internal-rotation: 53.9 (6) and 301 (4) cm−1 for the trans and cis forms of the normal species, respectively, and 41.9 (6) and 309 (4) cm−1 for the trans and cis forms of the N–D species, respectively. Spectra of four trans isotopologues with 13C, 15N, or 18O singly-substituted in the internal-rotation A state were observed and analyzed to derive the rs structure of the trans form. For comparison with the experimental data, ab initio calculations were carried out at MP2/6-31G∗∗ level to derive molecular structure, potential barrier to CH3 internal rotation, and the energy difference between the cis and trans forms. An extensive coupling was found between the CH3 internal rotation and N–H out-of-plane bending, suggesting that the potential function for the CH3 internal-rotation deviates considerably from a simple cos(3α) form. The effects of the V6 term is briefly discussed.

Peptide molecules XCO–NYY′ are characterized by low potential barrier V3 to internal rotation of a methyl group substituted for X and/or Y. A most conspicuous example is acetamide, for which V3 was previously reported to be 25.043857(19) cm−1 [8] . The present study intended to clarify why V3 is so low in acetamide, by examining the effect of the out-of-plane bending or inversion of the amino group on the molecular structure through deuterium substitution for amino hydrogens. The potential barrier V3 in acetamide was found to decrease by 2.630, 2.986, and 5.532 cm−1, when H′s at cis, trans, and both positions in the amino group were replaced by deuterium atoms, respectively. The reduction was proportional to the effective mass of the out-of-plane bending mode of the amino group (hereafter referred to as the amino inversion), which was in turn ascribed to the change in electronic resonance character of the peptide linkage. The amino inversion is coupled with the CH3 internal rotation, producing an interaction term proportional to τ sin 3α, where τ and α denote the amino inversion and methyl internal rotation angles, respectively. This coupling term, when the inversion is treated by second-order perturbation, yields a V6 term in the internal-rotation potential function of the methyl group, in agreement with the finding of Ilyushin et al. [8] , who derived an unusually large V6 term of −10.044874(73) cm−1. It is quite interesting that even a small perturbation such as deuterium substitution causes a substantial change in electronic structure of the peptide linkage.

We have observed the infrared spectrum of (15)NO(3) by a high resolution Fourier transform infrared (FT-IR) spectrometer using the reaction of F atoms with H(15)NO(3). Five (2)E'-(2)A(2)' bands are identified in the 1850-3150 cm(-1) region. The rotational analyses indicate that these bands have the lower state in common, which coincides with the ground state of planar D(3h) symmetry. The upper (2)E' states more or less suffer from perturbations by close-lying dark states. Among them, those of the 2004, 2128, and 2492 cm(-1) bands are analyzed to determine molecular parameters in these states by fixing the ground-state constants to those derived by a combination difference method. The spin-orbit and Coriolis coupling constants in the (2)E' states are substantially different for different vibronic states. The vibrational assignments of NO(3) in the ground electronic state are discussed using experimental data heretofore available, supplemented by those obtained by the present study.

The rotational spectra of three isotopomers of the Ar–dimethyl sulfide (DMS) complex – normal, 34 S, and 13 C species – were measured in the frequency region from 3.7 up to 24.1 GHz by Fourier transform microwave spectroscopy. The normal species yielded 43 a -type and 79 c -type transitions. No Ar tunneling splitting was observed, while many transitions were split by the internal rotation of the two methyl tops of the DMS unit. In cases where the K -type splitting was close to that due to methyl internal-rotation, several forbidden transitions were observed that followed b -type selection rules. All of the observed transition frequencies were analyzed simultaneously using a phenomenological Hamiltonian also used in previously published work describing the Ar–dimethyl ether (DME) and Ne–DME complexes. The rotational and centrifugal distortion constants and the potential barrier height to methyl-top internal rotation, V 3 , were determined. The rotational constants were consistent with an Ar–DMS center of mass (cm) distance of 3.796 (3) A and a S–cm–Ar angle of 104.8 (2)°. The V 3 potential barrier obtained, 736.17 (32) cm −1 , was 97.8% of the DMS monomer barrier. By assuming a Lennard–Jones-type potential, the dissociation energy was estimated to be 2.4 kJ mol −1 , which was close to the value for Ar–DME, 2.5 kJ mol −1 .

The fine and hyperfine structure in a free radical containing a methyl group is examined by paying special attention to the effects of the methyl group internal rotation on the fine and hyperfine interactions. The effects are taken into account by expanding pertinent constants describing couplings among angular momenta of electron and nuclear spins, internal rotation and overall rotation in terms of the internal rotation angle. The three-fold symmetry of the methyl internal rotation potential is lifted to some extent by fine and hyperfine interactions. The formulation thus developed is applied to the analysis of Fourier transform microwave spectra of the acetyl radical, and the potential barrier to internal rotation [139.958 (18) cm−1] and fine and hyperfine interaction constants are determined precisely.

The ground-state rotational spectra of the dimethyl sulfide-dimethyl ether (DMS-DME) and the ethylene oxide-ethylene sulfide (EO-ES) complexes were observed by Fourier transform microwave spectroscopy, and a-type and c-type transitions were assigned for the normal, (34)S, and three (13)C species of the DMS-DME and a-type and b-type transitions for the normal, (34)S, and two (13)C species of the EO-ES complexes. The transition frequencies measured for both the complexes were analyzed by using an S-reduced asymmetric-top rotational Hamiltonian. The rotational parameters thus derived for the DMS-DME were found to be consistent with a structure of Cs symmetry with the DMS bound to the DME by two C-H(DMS)···O and one S···H-C(DME) hydrogen bonds. Some high-Ka lines were found to be split, and we have interpreted these splittings in terms of internal rotations of the two methyl groups of the DMS and of the "free", i.e., outer group, of the DME. Some forbidden transitions were also observed in cases where Ka = 3 levels were involved, for the DMS-DME complex in the internal-rotation E state. The barrier height, V3, to internal rotation of the CH3 in the DME thus derived is smaller than that of the DME monomer, while the V3 of the CH3 groups in the DMS is nearly the same as that of the DMS monomer. For the EO-ES complex, the observed data were interpreted in terms of an antiparallel structure of Cs symmetry with the EO bound to the ES by two C-H(ES)···O and two S···H-C(EO) hydrogen bonds. An attempt was also made to observe a-type transitions of the DMS dimer without success. We have applied a natural bond orbital analysis to the DMS-DME and EO-ES to calculate the stabilization energy CT (= ΔEσσ*), which was correlated closely with the binding energy as found for other related complexes.

In view of the importance of the peptide linkage in structural biology, we have carried out intensive investigations on peptide molecules consisting of a peptide linkage with one or two substituents in the gas phase by Fourier transform microwave spectroscopy, paying special attention to the internal rotation of the substituents relative to the central linkage framework. We have found that, in sharp contrast with the stiff structure around the central C-N bond of the linkage, the internal rotations of the substituents are of low frequency and thus of large amplitude and are extremely susceptible to their local environment such as the presence of other substituents.

高分解能分子スペクトルデータベースHRMSDBの開発を開始した。一部を産業技術総合研究所RIODB(http://www.aist.go.jp/RIODB/hrmsdb/index.html)で公開したので概要を報告する。HRMSDBは、高分解能分子スペクトルから得られる分子の構造、回転定数他をデータベースとして公開することを目的とした文献データベースであり、著者のひとりである廣田栄治が1950年から2004年までに収集した、高精度な実験的・理論的スペクトルに関する約20,000の論文をそれぞれノート１ページほどに要約し、データベースとしてまとめた物である。

A peptide molecule: N -ethylformamide HCONHCH 2 CH 3 (NEFA) was investigated by Fourier transform microwave spectroscopy in order to determine molecular structure, potential barrier to methyl internal rotation, and nuclear quadrupole coupling constant of the nitrogen atom. All the three ( a , b and c ) types of transitions were observed; they were split into hyperfine structure components due to nitrogen nuclear quadrupole coupling. The rotational constants of NEFA were determined to be A =9904.8373(6), B =3521.0995(2) and C =2984.9808(2) MHz, with three standard deviations in parentheses. The inertial defect Δ = I cc − I aa − I bb was calculated from the rotational constants to be −25.24492(2) uA 2 , which indicates the ethyl group to be bent out of the peptide linkage plane. A comparison of the observed rotational constants with those calculated by an ab initio molecular orbital method also led us to conclude that the most stable form of NEFA is trans - sc , a conformer with a nonplanar heavy atom skeleton. No evidence has so far been obtained for the existence of other conformers, as was the case for a related molecule: N -ethylacetamide. We have also observed spectra of five singly substituted isotopomers, three 13 C and one for each of 15 N and 18 O, from which we derived a partial r s structure, in fair agreement with an ab initio result.

1,1-Dimethylsilacyclobutane, abbreviated as DMSCB, was investigated by Fourier transform microwave spectroscopy, by paying special attention to two types of large-amplitude motions in the molecule: two-top internal rotation and four-membered ring puckering and also to the coupling between the two. In order to clarify the unique feature of the internal dynamics in DMSCB in detail, two independent approaches were employed, one being a combination of a standard two-top theory of internal rotation and an established theory of ring puckering and the other a theory of large-amplitude motions developed by Hougen and his collaborators. In accordance with predictions by the two approaches based on symmetry consideration, the observed rotational spectra were found split into eight (or six when AE/EA lines were not resolved) components, which were assigned to the two-top states of AA, AE, EA, and EE symmetry, each being further split by puckering into two: the symmetric and antisymmetric states. The analyses by two approaches gave spectroscopic results, which were in good agreement with each other. The spectroscopic data on the normal species, combined with those on Si and C isotopic species, yielded molecular structure parameters including the puckering angle (the dihedral angle between the CSiC and CCC planes) of 28.64° or 30.26° (two possible sets). The splitting between the two lowest puckering states was determined to be 11.90(22) MHz, which led, with the equilibrium puckering angle, to the potential barrier to puckering of 395.3 or 347.0 cm−1 for the two sets, respectively, which was slightly lower than the value 440 cm−1 in a “parent” molecule: silacylcobutane. The first-order terms of the coupling between CH3 internal rotation and overall rotation were converted to the barrier to internal rotation of 567.8 and 505.1 cm−1 in the AE (two methyl groups rotating in the same direction, as viewed from Si) and EA (two methyl groups rotating in the opposite direction) states, respectively, which corresponded to the torsional frequencies of 154 and 144 cm−1, at variance with the Raman data of 177 and 172 cm−1, previously reported in literature.

In order to clarify the dynamical aspects of the peptide structure, N -methylpropionamide (NMPA) was investigated as an example of peptide molecules: XCONHY (X=CH 3 CH 2 and Y=CH 3 for NMPA), paying special attention to the internal rotation of the two methyl groups. NMPA was found to have an almost planar skeleton with an extended syn / trans conformation, as indicated by the observed value of I aa + I bb − I cc , and its rotational spectra were interpreted in terms of group G 18 consisting of six symmetry species: A 1 , A 2 , E 1 , E 2 , E 3 , and E 4 . The A 1 and E 2 spectra were observed split in most of b -type transitions, yielding the internal-rotation potential barrier V 3 of 796 (21) cm −1 for CH 3 in the ethyl group referred to as C–CH 3 . The spectra of the three E species: E 1 , E 3 , and E 4 appeared several tens to thousands MHz apart from the corresponding A 1 spectra, suggesting the internal-rotation potential barrier of CH 3 bonded to the nitrogen, called N–CH 3 , to be quite low. In sharp contrast with the A 1 spectra, which were well fitted to the ordinary asymmetric-rotor spectral pattern, a few higher-order terms were required to reproduce the E 1 spectra, presumably because of the low N–CH 3 barrier. The spectral analysis thus performed, in fact, led to the V 3 of 80.06487 (14) cm −1 , an order of magnitude lower than that of C–CH 3 . The E 3 and E 4 spectra were found to form triplets with the corresponding E 1 lines at the center, and the E 3 – E 1 and E 4 – E 1 splittings were explained essentially by the contributions of the C–CH 3 internal rotation combined with the kinetic-energy coupling between the two methyl groups. The torsion around the C–C bond between the ethyl and carbonyl groups was suggested by an ab initio calculation to be of double minimum nature, but the observed A 1 spectra did not show any indication of such a double-minimum potential for the C–C torsion, although the possibility of a small hump being present at a planar conformation could not be entirely eliminated. The present results on NMPA along with those obtained on other peptide molecules will be of some significance in clarifying important problems of structural biology such as protein folding and signal transfer through biological systems.

Two sets of vibrational satellites have been observed in the rotational spectrum of sodium tetrahydroborate NaBH4, and have been assigned to the non-degenerate, Na—BH4 stretching and the degenerate BH4 rocking (or internal rotation) states. The observation was extended from the J = 11 ← 10 up to J = 20 ← 19 transitions. The vibrational satellites showed anomalous K structure; higher-K lines of the non-degenerate state appeared at higher frequencies, in reverse to those of the ground state, whereas the spectra in the degenerate state exhibited a K pattern similar to but somewhat more widely spread than that of the ground state. These anomalies are ascribed to the Coriolis interaction between the two excited vibrational states. The spectra observed were analysed using a C3v symmetric-top rotational Hamiltonian, which took into account the Coriolis interaction explicitly. The A rotational constants, the energy difference δE between the two interacting vibrational states, and the first- and second-order Corio...

Rotationally resolved high-resolution fluorescence excitation spectra of (14)NO3 radical have been observed for the 662 nm band, which is assigned as the 0-0 band of the B̃(2)E' ←X̃(2)A2' transition, by crossing a single-mode laser beam perpendicularly to a collimated molecular beam. More than 3000 rotational lines were detected in 15,070-15,145 cm(-1) region, but it is difficult to find the rotational line series. Remarkable rotational line pairs, whose interval is about 0.0246 cm(-1), were found in the observed spectrum. This interval is the same amount with the spin-rotation splitting of the X̃(2)A2' (υ = 0, k = 0, N = 1) level. From this interval and the observed Zeeman splitting up to 360 G, seven line pairs were assigned as the transitions to the (2)E'(3/2) (J' = 1.5) levels and 15 line pairs were assigned as the transitions to the (2)E'(1/2) (J' = 0.5) levels. From the rotational analysis, we recognized that the (2)E' state splits into (2)E'(3/2) and (2)E'(1/2) by the spin-orbit interaction and the effective spin-orbit interaction constant was roughly estimated as -21 cm(-1). From the number of the rotational line pairs, we concluded that the complicated rotational structure of this 662 nm band of (14)NO3 mainly owes to the vibronic interaction between the B̃(2)E' state and the dark Ã(2)E″ state through the a2″ symmetry vibrational mode.

The rotational spectrum of the deuterated isopropanol (CH(3))(2)CHOD has been observed by Fourier transform microwave spectroscopy and analyzed to yield tunneling splitting of 4431.4613 (17) MHz, between the antisymmetric and the symmetric gauche forms, which is much larger than the 2400 MHz estimated from the internal-rotation potential function reported in the literature. The potential function for the OH internal rotation has been examined in view of the discrepancy between the observed and estimated tunneling splitting, and it was accounted for by taking into account isotope effects on the potential constants. The deuterium quadrupole coupling effect has been included together with the Coriolis terms in the off-diagonal block of the Hamiltonian matrix for the gauche form. The deuterium quadrupole coupling constants obtained for the trans form were employed to calculate the components of the coupling constants as functions of the internal-rotation angle, and the components at around 120 degrees were compared with the values observed for the gauche form, thereby leading to unambiguous determination of the signs of the constants in the off-diagonal block; the signs are not obtainable from an ordinary analysis of the rotational spectra. The chirality of the gauche form was discussed by placing special emphasis on the effect of intermolecular interactions between two chiral molecules. Copyright 2001 Academic Press.

The microwave spectrum of CsO has been observed and analyzed, not only in the ground vibrational state, but also in the v=1–3 excited vibrational states. The CsO radical was generated by the reaction of N2O with Cs vapor, which was produced by the reaction of Li metal with CsCl at 500–530 °C. The observed spectra were found to conform to those expected for a 2Σ diatomic molecule, thereby establishing the ground electronic state of CsO to be of 2Σ. The observed rotational and centrifugal distortion constants yielded the equilibrium bond length and the harmonic vibrational frequency to be 2.300 745 (16) A and 356.78 (11) cm−1, respectively, based on the Born–Oppenheimer approximation. A careful examination of the observed spectral pattern definitely concluded that the spin-rotation interaction constant was positive, at variance with the expectation from a simple 2Σ/2Π two-states interaction. This observation was interpreted by assuming positive contributions from higher excited electronic states which super...

Microwave spectra of Ar– 28 SiH 4 , Ar– 29 SiH 4 , Ar– 30 SiH 4 , and Ar– 28 SiD 4 were recorded using a pulsed molecular beam Fourier transform microwave spectrometer. The K = 0 and K = 1 components of the J = 3 ← 2 through the J = 7 ← 6 transitions were measured and assigned in the 9–24 GHz region. For the primary 28 Si isotopic species, Ar– 28 SiH 4 and Ar– 28 SiD 4 , a K = 0, A symmetry, a K = 0, F symmetry, a doubly degenerate K = 1, E symmetry, and an l / K -doubled, K = 1, F symmetry rotational progression are observed at the ≈1 K rotational temperature of the supersonic expansion. The rotational constants for the K = 0, A state for Ar– 28 SiH 4 and Ar– 28 SiD 4 are B = 1700.40624(9) MHz and 1630.687073(22) MHz and the centrifugal distortion constants are D J = 29.089(3) and 20.0198(8) kHz and H J = −1.91(3) and −0.851(8) Hz, respectively, where type A expanded uncertainties with a coverage factor, k = 3, are given here and elsewhere. The values of the rotational constants for the K = 0, A , and F states and for the K = 1, E state are in good agreement with the infrared-determined values for Ar– 28 SiH 4 . The measured linear Stark effect of the E -state transitions was analyzed to give a dipole moment of 9.24(8) × 10 −32 C · m [0.0277(2) D].

The infrared spectrum of SiH2 was observed in the 5 μm region by using diode laser spectroscopy, and the three bands ν1, 2ν2, and ν3 were recorded and assigned. A separate analysis of the three bands yielded the band origins, 1995.9280, 1987.6938, and 1992.816 cm−1, respectively, thereby establishing that ν1 is higher than 2ν2, contrary to the result of a previous matrix study. The anharmonic resonances, both ν1/2ν2 Fermi and 2ν1/2ν3 Darling–Dennison, which were observed in the laser induced fluorescence spectra previously reported, were reanalyzed by removing the condition ν1

The rotational spectra of 85RbO in the ground- and the first excited vibrational states and of 87RbO in the ground vibrational state were observed in the millimeter- and submillimeter-wave region. The RbO radical was generated in a high-temperature absorption cell by the reaction of N2O with Rb vapor, which was produced in the cell by heating a mixture of RbCl and lithium metal to 500–550 °C. Analysis of the observed spectra yielded the rotational and centrifugal distortion constants, spin–rotation interaction constants, and hyperfine interaction constants. The bond length and the vibrational frequency were calculated from the rotational and centrifugal distortion constants to be 2.254 193 1 (15) A and 387.22 (20) cm−1, respectively, for 85RbO. The ground electronic state of RbO was confirmed to be 2Σ, and the low-lying 2Π state was estimated to be located at 650–700 cm−1 above the ground state by using a second-order perturbation expression with the vibrational energy in the denominator for the spin–rota...

Seven transient molecules, of which four are expected to play important roles primarily in deposition processes in plasma and three mainly in etching processes, were discussed on a basis of high-resolution vibration-rotation infrared spectra. A simple modification of infrared diode laser spectroscopy as referred to as kinetic spectroscopy allowed us to observe such spectra as functions of time. Applications of this spectroscopy to the diagnosis of three plasma processes were described to illustrate the potentiality as well as the versatility of the method: silane RF discharge plasma, methane RF and methanol ECR plasmas, and ECR etching plasma.

The infrared spectrum of the NO 3 radical is observed by high-resolution Fourier transform spectroscopy, infrared and near-infrared diode laser spectroscopy, and the vibrational assignments of the observed bands are discussed. The molecular constants of NO 3 in the ground electronic 2 A 2 ′ state have been re-determined by using observed combination differences derived from the infrared spectrum between 1300 and 8000 cm −1 , as follows, B =0.458 5485(63), D N =0.1113(12), D NK =−0.2121(27)×10 −5 , ϵ bb =−0.016 49(13) cm −1 , with one standard deviation in parentheses. The 1927 cm −1 band observed by a Fourier transform spectrometer has been newly analyzed, and molecular constants of the upper state are determined.

The rotational spectrum of the SiFCl molecule in the ground vibronic state was observed for the first time in the frequency region from 340 to 356 GHz. The analysis of the observed spectrum, which consisted of both a-type and b-type transitions, yielded rotational constants and centrifugal distortion constants of the 35Cl and 37Cl isotopic species in the ground state. The harmonic force field of SiFCl was derived from the centrifugal distortion constants and the inertial defects determined for both isotopic species and was used to calculate the vibrational frequencies of the molecule. The average structure in the ground vibrational state was determined to be r z ( SiF ) = 1.5960 A , r z ( SiCl ) = 2.0714 A , ϑz(FSiCl) = 100.85° and σr z ( SiCl )[ 35 Cl  37 Cl difference ] = 0.000065 A by using the observed rotational constants and the harmonic force field derived in the present study.