Laboratory measurements and astronomical search for cyanomethanimine

TL;DR

This study extended laboratory measurements of cyanomethanimine's rotational spectrum into the millimeter/submillimeter range and conducted astronomical searches in star-forming regions, setting upper limits on its abundance.

Contribution

The paper provides improved spectroscopic data for cyanomethanimethine and reports the first astronomical search for it in Sun-like-star forming regions, establishing upper abundance limits.

Findings

No detection of cyanomethanimine in surveyed regions.

Established upper limits on its column density and abundance.

Extended spectroscopic data up to 700 GHz for future searches.

Abstract

C-cyanomethanimine (HNCHCN), existing in the two $Z$ and $E$ isomeric forms, is a key prebiotic molecule, but, so far, only the $E$ isomer has been detected toward the massive star-forming region. Sagittarius B2(N) using transitions in the radio wavelength domain. With the aim of detecting HNCHCN in Sun-like-star forming regions, the laboratory investigation of its rotational spectrum has been extended to the millimeter-/submillimeter-wave (mm-/submm-) spectral window in which several unbiased spectral surveys have been already carried out. High-resolution laboratory measurements of the rotational spectrum of C-cyanomethanimine were carried out in the 100-420 GHz range using a frequency-modulation absorption spectrometer. We then searched for the C-cyanomethanimine spectral features in the mm-wave range using the high-sensitivity and unbiased spectral surveys obtained with the IRAM 30-m antenna in the ASAI context, the earliest stages of star formation from starless to evolved Class I objects being sampled. For both the $Z$ and $E$ isomers, the spectroscopic work has led to an improved and extended knowledge of the spectroscopic parameters, thus providing accurate predictions of the rotational signatures up to $\sim$700 GHz. So far, no C-cyanomethanimine emission has been detected toward the ASAI targets, and upper limits of the column density of $\sim$ 10$^{11}$--10$^{12}$ cm$^{-2}$ could only be derived. Consequently, the C-cyanomethanimine abundances have to be less than a few 10$^{-10}$ for starless and hot-corinos. A less stringent constraint, $\leq$ 10$^{-9}$, is obtained for shocks sites. The combination of the upper limits of the abundances of C-cyanomethanimine together with accurate laboratory frequencies up to $\sim$ 700 GHz poses the basis for future higher sensitivity searches around Sun-like-star forming regions.