Spectroscopy of Interstellar Internal Rotors: An Important Tool for Investigating Interstellar Chemistry

Abstract

This paper is a review of molecules with internal rotors detected or tentatively detected with upper limits in the interstellar medium. Internal rotor molecules containing one or two methyl groups are present at each of the different phases leading to stellar and planetary formation, from the molecular clouds to the star and its planets. They are also found in comets and asteroids. They represent a ubiquitous hydrogen-rich substituent in many complex organic molecules. This paper shows how high resolution spectra (mainly in the microwave, millimeter and sub-millimeter wave range) are analyzed in the laboratory and what theoretical methods can be used to properly reproduce the spectra. We also present a range of examples of important methyl rotors studied and how they can be used as tools to study the chemistry of interstellar medium.

The effects of proton tunneling, 14N quadrupole coupling, and methyl internal rotations in the microwave spectrum of ethyl methyl amine

“…This is most probably because of the lack of an important step towards the detections of new molecules in the ISM, which is the laboratory investigation of rotational spectra of those molecules, as pointed out in a recent review by Kleiner. 7 So far, the spectra of only three linear aliphatic secondary amines have been studied by high resolution microwave spectroscopy, which are dimethyl amine 8 , ethyl methyl amine (EMA), 9 and diethyl amine. 10 This class of molecules is particularly interesting for spectroscopic researches, featuring a multitude of different effects that can occur in the microwave spectra.…”

Internal rotation arena: Program performances on the low barrier problem of 4-methylacetophenone

“…In contrast, this approach does not work for large values of , typically found in small molecules composed of only a few atoms, like methanol with a value of 𝜌 = 0.81 [24]. 145 As briefly mentioned above and shown in some reviews on LAMs [1,2,25], each internal rotation program has its own advantages and drawbacks. The advantage of the CAM together with the user-friendly application of XIAM has made XIAM one of the most popular codes used in the spectroscopic community.…”

“…The advantage of the CAM together with the user-friendly application of XIAM has made XIAM one of the most popular codes used in the spectroscopic community. A 150 drawback of XIAM is its failure when it comes to low barrier cases observed in many previous studies [26][27][28][29][30] (𝑠 = 0.3 to 20.8), which was often claimed to be due to the negligence of interaction between the different torsional states [25].…”

Astrochemical Pathways to Complex Organic and Prebiotic Molecules: Experimental Perspectives for In Situ Solid-State Studies

“…To date, more than 200 species have already been detected in the gas phase while only about 10 molecules have been spectroscopically identified in the solid state (e.g., Cologne Database for Molecular Spectroscopy and [ 3 ]). The variety, abundance, and distribution of gas-phase and solid-state COMs already detected or tentatively detected in space have been increasing in the last decades, touching various astronomical environments, from interstellar clouds, protostars, and protoplanetary disks (e.g., [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ]) to the outer solar system, where COMs and prebiotic species have already been detected in several comets (e.g., [ 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ]). To give the reader an idea, the list of these COMs includes but is not limited to: acetaldehyde (CH 3 CHO), ethanol (CH 3 CH 2 OH), formamide (HCONH 2 ), glycine (NH 2 CH 2 COOH), and urea (H 2 NCONH 2 ).…”