Millimeter-wave spectroscopy of hydantoin, a possible precursor of glycine

Abstract

Context. Hydantoin (Imidazolidine-2, 4-dione, C 3 H 4 N 2 O 2 ) is a five-membered heterocyclic compound that is known to arise from prebiotic molecules such as glycolic acid and urea, and to give the simplest amino acid, glycine, by hydrolysis under acidic condition. The gas chromatography combined with the mass spectrometry of carbonaceous chondrites lead to the detection of this molecule as well as several kinds of amino acids. Aims. The lack of spectroscopic information, especially on the rotational constants, has prevented us from conducting a search for hydantoin in interstellar space. If a rotational temperature of 100 K is assumed as the kinetic temperature of a star-forming region, the spectral intensity is expected to be at its maximum in the millimeter-wave region. Laboratory spectroscopy of hydantoin in the millimeter-wave region is the most important in providing accurate rest frequencies to be used for astronomical research. Methods. Pure rotational spectra of hydantoin were observed in the millimeter-wave region using the frequency modulated microwave spectrometer at Toho University. Solid hydantoin was heated to around 150• C to provide appropriate vapor pressure. Quantum chemical calculations suggest that the permanent dipole moment of this molecule lies almost along the b-molecular axis, so that spectral search for b-type R-branch transition has been conducted. Results. Rotational and centrifugal distortion constants up to the fourth order for the ground vibrational state of hydantoin were accurately determined by measuring 161 b-type transitions in the frequency range between 90 and 370 GHz. In addition, we succeeded in assigning 230 satellite lines, which were attributed to the two vibrationally excited states. The spectral intensity ratio of these lines indicates that these states correspond to the low-lying (approximately 150 cm −1 above the ground state) vibrational modes. Conclusions. The frequency catalog of hydantoin in the millimeter-wave range was created for the ground state and for the two low-lying excited states, and are ideal for a future astronomical research. The 1σ frequency accuracy is lower than 100 kHz for the lines with upper-state energy below 200 cm −1 , corresponding to a velocity resolution of 0.1 km s −1 at 300 GHz

Where's water? The many binding sites of hydantoin

“…Because of this, the hyperfine splitting eventually collapses for rotational transitions with increasing J value. In the millimeter-wave study on hydantoin by Ozeki et al, 13 no hyperfine structure was observed because of the high J rotational quantum numbers involved. The low-frequency range of the COMPACT spectrometer probes the lowest rotational transitions, so that, together with the high resolution of the spectrometer, the hyperfine structure is well resolved.…”

“…11,12 The first high-resolution laboratory spectroscopy study of hydantoin in the gas phase was reported in 2017 using millimeter-wave (mmw) spectroscopy in the frequency range 90 to 370 GHz. 13 Molecular constants for the ground state and two low-lying vibrationally excited states were reported, which can be useful for high frequency radio astronomical observations where molecular vibrationally excited states can be observed. Spectral line catalogues for these states provide useful rest frequencies for searches of hydantoin in interstellar space.…”

Rotational spectroscopy of imidazole: Accurate spectroscopic information for three vibrationally excited states and the heavy-atom isotopologues up to 295 GHz

“…The dierence in the SNR between the experimental spectra of the imidazole ground state and the lowest energy vibrationally excited state, 21 , is a factor of 10 at approximately 300 K. This factor matches well with the assumed Boltzmann distribution at 300 K, which suggests a population dierence between the vibronic ground state and the 21 state of a factor of twelve. For hydantoin, a structurally related molecule to imidazole, for which a structural comparison is laid out in the next section, the ratio of the SNR of the ground state to the first vibrationally excited state (140 cm 1 above the ground state) was found to be 1:0.6 [44]. This intensity ratio was reported for the experiment at 420 K [44], and the Boltzmann population dierence at that temperature is a factor of 1.5.…”

“…For hydantoin, a structurally related molecule to imidazole, for which a structural comparison is laid out in the next section, the ratio of the SNR of the ground state to the first vibrationally excited state (140 cm 1 above the ground state) was found to be 1:0.6 [44]. This intensity ratio was reported for the experiment at 420 K [44], and the Boltzmann population dierence at that temperature is a factor of 1.5. This reinforces experimentally the higher relative energies of the imidazole vibrationally excited states.…”

Millimetre-wave laboratory study of glycinamide and search for it with ALMA toward Sagittarius B2(N)

“…Some of them, such as methylamine (Kaifu et al 1974), aminoacetonitrile (Belloche et al 2008), and hydroxylamine (Rivilla et al 2020) have been already detected. Rotational spectroscopic studies of potential glycine precursors hydantoin (Alonso et al 2017;Ozeki et al 2017) and hydantoic acid (Kolesniková et al 2019) were reported recently. Sanz-Novo et al (2019) further computed the spectroscopic properties of glycine isomers of which methyl carbamate (Marstokk & Møllendal 1999;Bakri et al 2002;Ilyushin et al 2006;Groner et al 2007) and glycolamide (Maris 2004;Sanz-Novo et al 2020) were studied by microwave and millimetre wave spectroscopies that enabled their searches in the ISM (Sanz-Novo et al 2020;Sahu et al 2020).…”