Search

The rotational spectra of the two stable conformers syn - and gauche -propanal (CH 3 CH 2 CHO) were studied in the millimeter and submillimeter wave regions from 75 to 500 GHz with the Cologne (Sub-)Millimeter wave Spectrometer. Furthermore, the first excited states associated with the aldehyde torsion and with the methyl torsion, respectively, of the syn -conformer were analyzed. The newly obtained spectroscopic parameters yield better predictions, thus fulfill sensitivity and resolution requirements in new astronomical observations in order to unambiguously assign pure rotational transitions of propanal. This is demonstrated on a radio astronomical spectrum from the Atacama Large Millimeter/submillimeter Array Protostellar Interferometric Line Survey (ALMA-PILS). In particular, an accurate description of observed splittings, caused by internal rotation of the methyl group in the syn -conformer and by tunneling rotation interaction from two stable degenerate gauche -conformers, is reported. The rotational spectrum of propanal is of additional interest because of its two large amplitude motions pertaining to the methyl and the aldehyde group, respectively. [ABSTRACT FROM AUTHOR]

Acetone-13C 1 is a complex organic molecule with two internal methyl (-CH 3) rotors having relatively low effective barriers to internal rotation of about 249 cm − 1. This leads to two low-lying torsional modes and five internal rotation components resulting in a dense and complicated spectrum. In this study, measurements of acetone-13C 1 were performed with an isotopically enriched sample in the frequency range 37 – 1102 GHz. Predicted spectra of acetone-13C 1 created with ERHAM allow for future radio astronomical searches. Loomis-Wood plots are one approach to improve and fasten the analysis of such crowded spectra. In this study, the new Loomis-Wood software LLWP was used for fast and confident assignments. LLWP focuses on being user-friendly, intuitive, and applicable to a broad range of assignment tasks. The software is presented here and can be downloaded from llwp.astro.uni-koeln.de. [Display omitted] [ABSTRACT FROM AUTHOR]

A detailed analysis of (sub-)millimeter-wave spectra of the vibrational ground state (υ = 0) combined with the energetically lowest excited vibrational state ( υ 24 = 1 ; aldehyde torsion) of gauche -propanal (g - C2H5CHO) up to 500 GHz is presented. Both vibrational states, υ = 0 and υ 24 = 1 , are treated with tunneling rotation interactions between their two respective tunneling states, which originate from two stable degenerate gauche -conformers; left- and right-handed configurations separated by a small potential barrier. Thanks to double-modulation double-resonance (DM-DR) measurements, important but weak c -type transitions connecting the tunneling states could be unambiguously assigned. In addition, Coriolis interaction as well as Fermi resonance between the two vibrational states needed to be taken into account to derive fits with experimental accuracy using Pickett's SPFIT program in a reduced axis system (RAS). Based on the rotational analysis, the fundamental vibrational frequency ν 24 of gauche -propanal is redetermined to 68.75037(30) cm−1. [Display omitted] • Combined rotational analysis of the ground (v = 0) and first excited aldehyde torsion (v 24 = 1). • Treatment of tunneling-rotation interaction in a reduced axis system (RAS). • Description of Coriolis interaction and Fermi resonance between vibrational states. • Re-determination of the fundamental frequency v 24 = 68.75037(30) cm-1. [ABSTRACT FROM AUTHOR]

A new millimeter- to millimeter-wave double-modulation double-resonance (MMW-MMW DM-DR) scheme has been applied to record spectra of two astronomically relevant complex organic molecules (COMs), propanal (C 2 H 5 CHO) and ethyl cyanide (C 2 H 5 CN), to demonstrate advantages of the DM-DR experimental technique. The DR technique helps to identify target transitions in a forest of lines and the implementation of a DM procedure (modulation of the pump and probe source) allows for confusion- and baseline-free spectra containing only the line(s) of interest. In particular the unambiguous assignment of weak and blended transitions in very dense MMW spectra is highlighted. Details of the observed Autler–Townes line splitting and possible future applications, such as automated analyses and adaptions of DM-DR methods to other experimental setups, are discussed. [Display omitted] • Directly observable Autler–Townes line splitting in the MMW region. • Establishing a double-modulation double-resonance (DM-DR) scheme. • Recording confusion- and baseline-free spectra. • Unambiguously assign weak and blended transitions. [ABSTRACT FROM AUTHOR]

[Display omitted] • CP-FTmmw and 2f modulation spectroscopy on propylene oxide from 75 to 950 GHz. • Analysis of the first excited torsional state, ν 24 , using ERHAM and XIAM. • Using XIAM, the internal barrier height was determined to be 898.6611(894) cm−1. • Analysis allowed for a precise description of methyl top structure and ρ -axis. • Accurate line lists and predictions to 1 THz delivered for astrophysical searches. The first excited torsional state of the chiral molecule propylene oxide, CH 3 C 2 H 3 O , is investigated from millimeter up to sub-millimeter wavelengths (75–950 GHz). The first excited vibrational mode of propylene oxide, υ 24 , is analysed using the programs ERHAM and XIAM. Rotational constants and tunneling parameters are provided, and a description of the A-E splittings due to internal rotation is given. Furthermore, the potential barrier height to internal rotation, V 3 , is determined to be V 3 = 898.6611 (894) cm - 1 . Our results are compared with quantum chemical calculations and literature values. We present a line list of the dense spectrum of the first excited torsional state of propylene oxide in the (sub-) millimeter range. Our results will be useful for further studies of chiral molecules in vibrationally excited states and will enable astronomers to search for rotational transitions originating from υ 24 of propylene oxide in interstellar space. [ABSTRACT FROM AUTHOR]

• First high-resolution infrared study of ethyl cyanid. • Four energetically lowest vibrational fundamentals studied. • Global fits of infrared and pure rotational spectra performed. • Strong vibrational satellites towards high mass star forming region assigned. The high resolution vibrational spectrum of ethyl cyanide (C 2 H 5 CN) has been investigated in the far-IR using synchrotron-based Fourier transform spectroscopy. The assignment was performed using the Automated Spectral Assignment Procedure (ASAP) allowing accurate rotational energy levels of the four lowest fundamental vibrations of the species, namely the v 13 = 1 @ 205.934099(8) cm−1, v 21 = 1 @ 212.141101(8) cm−1, v 20 = 1 @ 372.635293(15) cm−1, and v 12 = 1 @ 532.699617(16) cm−1 states, to be determined. The analysis not only confirms the applicability of the ASAP in the treatment of (dense) high-resolution infrared spectra but also reveals some of its limitations. Complementary to the infrared study, the pure rotational spectrum of C 2 H 5 CN was also studied in selected frequency ranges from 75 to 255 GHz. New observations of a prototypical high-mass star-forming region, G327.3–0.6, performed with the Atacama Large Millimeter Array show that vibrational satellites of C 2 H 5 CN can be very intense, of order several tens of Kelvin in units of brightness temperature. [ABSTRACT FROM AUTHOR]