Spectroscopic Identification and Bonding Properties of HNCOCa+:a Matrix Isolation and Computational Study
Metal(iso)cyanides dominate the molecular inventory of metal-bearing species in the in-terstellar medium.Their oxide counterparts,metal(iso)cyanates,have potential as inter-stellar molecules and have received signifi-cant attention.However,cationic complexes HNCOM+as precursors to metal(iso)cyanates are rarely studied.Herein,we investigated HNCOCa+by exploiting in-frared spectrometry with isotopic substitu-tions and quantum chemical calculations.For comparison,the light and heavy alkaline earth metal cationic complexes HNCOBe+and HNCOBa+were also explored.HNCOCa+and HNCOBe+rather than HNCOBa+can be experimentally generated by the reactions of metal cations with HNCO.The observed antisymmetric and symmetric NCO stretching vi-brations in HNCOCa+(2362.6 and 1330.4 cm-1)are higher than those in free HNCO(2268.5 and 1320.3 cm-1)but lower than those in HNCOBe+(2426.4 and 1355.2 cm-1).These shifts can be explained by the charge polarization within the NCO fragment in HNCOBe+and HN-COCa+.Bonding analysis suggests that HNCO-Be+bond favors covalent character(54％)while HNCO-Ca+bond has higher electrostatic character(57％).The dominant electrostatic interaction(64％)in HNCO-Ba+bond results in the low bond energy,which might account for its absence in experiments.
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