Rotational spectroscopy of isotopic oxirane, c-C2H

Rotational spectroscopy of mono-deuterated oxirane ($c$-C$_2$H$_3$DO) and its detection towards IRAS 16293$-$2422 B

“…The molecule has C 2v symmetry with its dipole moment of 1.90 D along the b-axis (Cunningham et al 1951). This value includes a small upward correction of 0.02 D (Müller et al 2022) caused by the difference of the OCS reference value used in Cunningham et al (1951) compared to more modern values (Tanaka et al 1985;Lahaye et al 1986). The main isotopologue is an asymmetric top rotor of the oblate type with κ = (2B − A − C)/(A − C) = +0.4093 which is quite far from the oblate symmetric limit of +1.…”

“…In the case of oxirane all other common combinations of reduction and representation, the S reduction in the oblate III l representation and the A and S reductions in the prolate I r representation yielded satisfactory fits albeit the A reduction in I r required two parameters less than the two combinations involving S reductions. The A reduction in I r was in fact the preferred choice in several studies on c-C 2 H 4 O (Medcraft et al 2012;Müller et al 2022) and c-C 2 H 3 DO (Puzzarini et al 2014;Albert et al 2019). We used the scaled parameters from a quantum-chemical calculation (Puzzarini et al 2014) as starting values in our present study on c-C 2 H 3 DO exactly for this reason.…”

“…Oxirane (c-C 2 H 4 O) is also known as epoxyethane, ethylene oxide, dimethylene oxide and oxacyclopropane. Its rotational spectrum was studied quite extensively (Hirose 1974b;Creswell & Schwendeman 1974;Pan et al 1998;Medcraft et al 2012;Müller et al 2022). The molecule has C 2v symmetry with its dipole moment of 1.90 D along the b-axis (Cunningham et al 1951).…”

“…We refitted the previous c-C 2 H 3 DO data (Hirose 1974a;Albert et al 2019) in order to derive transition frequencies, their uncertainties and intensities for our present laboratory studies. We assumed 50 kHz for the data from Hirose (1974a) in analogy to the experimental lines of the main isotopic species (Hirose 1974b) from the same author and based on our judgement (Müller et al 2022) of the c-C 13 CH 4 O and c-C 2 H 4 18 O data from Hirose (1974a). Two transition frequencies from that work with large residuals of 0.20 MHz and 0.72 MHz were omitted.…”

“…Several spectroscopists view Watson's A reduction in an oblate representation as the natural choice to fit an asymmetric rotor of the oblate type. Several studies on molecules such as H 2 S (Yamada & Klee 1994), dimethylsulfoxide (Margulès et al 2010), the lowest energy conformer of 2-cyanobutane or the main isotopologue of oxirane (Müller et al 2022) revealed that this choice of reduction and representation is frequently a rather poor one. All other choices yielded better fits or required fewer parameters.…”