Maté B, Molpeceres G, Timón V, Tanarro I, Escribano R, Guillemin J C, Cernicharo J, Herrero V J
Instituto de Estructura de la Materia (IEM-CSIC), Serrano 121-123, 28006 Madrid, Spain.
Institut des Sciences Chimiques de Rennes, École Nationale Supérieure de Chimie de Rennes, CNRS, UMR 6226, 11 Allée de Beaulieu, CS 50837, 35708 Rennes Cedex 7, France.
Mon Not R Astron Soc. 2017 Oct 1;470(4):4222-4230. doi: 10.1093/mnras/stx1461. Epub 2017 Jun 12.
Methyl isocyanate has been recently detected in comet 67P/ Churyumov-Gerasimenko (67P/CG) and in the interstellar medium. New physicochemical studies on this species are now necessary as tools for subsequent studies in astrophysics. In this work, infrared spectra of solid CHNCO have been obtained at temperatures of relevance for astronomical environments. The spectra are dominated by a strong, characteristic multiplet feature at 2350-2250 cm, which can be attributed to the antisymmetric stretching of the NCO group. A phase transition from amorphous to crystalline methyl isocyanate is observed at ~ 90 K. The band strengths for the absorptions of CHNCO in ice at 20 K have been measured. Deuterated methyl isocyanate is used to help with the spectral assignment. No X-ray structure has been reported for crystalline CHNCO. Here we advance a tentative theoretical structure, based on Density Functional Theory (DFT) calculations, derived taking as a starting point the crystal of isocyanic acid. A harmonic theoretical spectrum is calculated then for the proposed structure, and compared with the experimental data. A mixed ice of HO and CHNCO was formed by simultaneous deposition of water and methyl isocyanate at 20 K. The absence of new spectral features indicates that methyl isocyanate and water do not react appreciably at 20 K, but form a stable mixture. The high CHNCO/HO ratio reported for comet 67P/CG, and the characteristic structure of the 2350-2250 cm band, make of it a very good candidate for future astronomical searches.
最近在67P/丘留莫夫－格拉西缅科彗星（67P/CG）和星际介质中检测到了异氰酸甲酯。现在有必要对该物质进行新的物理化学研究，作为后续天体物理学研究的工具。在这项工作中，已在与天文环境相关的温度下获得了固体CHNCO的红外光谱。光谱主要由2350 - 2250厘米处的一个强特征多重峰主导，这可归因于NCO基团的反对称伸缩。在约90K时观察到从非晶态到结晶态异氰酸甲酯的相变。已测量了20K时冰中CHNCO吸收的谱带强度。使用氘代异氰酸甲酯来辅助光谱归属。尚未报道结晶CHNCO的X射线结构。在此，我们基于密度泛函理论（DFT）计算提出一个暂定的理论结构，该结构以异氰酸晶体为起点推导得出。然后为所提出的结构计算一个谐波理论光谱，并与实验数据进行比较。通过在20K时同时沉积水和异氰酸甲酯形成了HO和CHNCO的混合冰。没有新的光谱特征表明异氰酸甲酯和水在20K时不会明显反应，而是形成稳定的混合物。67P/CG彗星报道的高CHNCO/HO比率以及2350 - 2250厘米波段的特征结构，使其成为未来天文搜索的一个非常好的候选对象。
