Laboratory spectroscopy of isobutene (M. Fatima+, 2023) ================================================================================ Millimeter and submillimeter spectroscopy of isobutene and its detection in the molecular cloud G+0.693. M. Fatima, H. S. P. Müller, O. Zingsheim, F. Lewen, V. M. Rivilla, I. Jiménez-Serra, J. Martín-Pintado, S. Schlemmer =References ? ================================================================================ ADC_Keywords: Interstellar medium ; Spectroscopy ; Molecular physics Keywords: Astrochemistry ; Techniques - spectroscopic ; Molecular data - ISM - molecules ; Radio lines - ISM ; ISM - individual objects - G+0.693-0.027 Abstract (includes Description): Isobutene ((CH3)2C=CH2) is one of the four isomers of butene (C4H8). After the detection of propene (CH3CH=CH2) toward TMC-1, and also in the warmer environment of the solar-type protostellar system IRAS 16293-2422, one of the next alkenes, isobutene, is thus a promising candidate to be searched for in space. We aim to extend the limited line lists of the main isotopologue of isobutene from the microwave to the millimeter region to obtain a highly precise set of rest frequencies and to facilitate its detection in the interstellar medium. Description: We investigated the rotational spectrum of the isobutene in the 35-370 GHz range using absorption spectroscopy at room temperature. Quantum-chemical calculations were carried out to evaluate vibrational frequencies. We determined new or improved spectroscopic parameters for isobutene up to sixth order distortion constant. These new results enabled its detection in the G+0.693 molecular cloud for the first time, where recently propene has also been found. The column density propene : isobutene ratio was determined to be about 3 : 1.The observed spectroscopic parameters for isobutene are accurate enough that calculated transition frequencies should be reliable up to 700 GHz. This will further help in observing it in other, warmer regions of the ISM. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . this file isobutene.txt 63 3751 Transitions included in the fit of isobutene ((CH3)2C=CH2) catalogue-file.txt 76 67617 Catalogue file up to 1 THz (J=99, T = 300 K) Generated from ERHAM program, with additional blanks -------------------------------------------------------------------------------- Byte-by-byte Description of file: isobutene.txt -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 2 I2 --- J' Upper state J quantum number 4- 5 I2 --- Ka' Upper state Ka quantum number 7- 8 I2 --- Kc' Upper state Kc quantum number 10-11 I2 --- J" Lower state J quantum number 13-14 I2 --- Ka" Lower state Ka quantum number 16-17 I2 --- Kc" Lower state Kc quantum number 19-29 F11.4 MHz FreqObs Observed transition frequency 31-37 F7.4 MHz (O-C) Observed minus calculated frequency 39-43 F5.3 MHz Uncer. Uncertainity used 45-46 I2 --- qq' (IS1,IS2) internal rotor components where 00 = A1A1, 01 = EE, 11 = A1E, 12 = EA1. 48-52 F5.2 --- wb Weight of the component in group of lines 54-60 F7.4 MHz I(O-C) Individual O-C residual for line consisting of several transitions 62-62 I1 --- Notes Source of data (reference) -------------------------------------------------------------------------------- References as follows: 1 = Gutowsky, H.S. & Germann, T. C. 1991, J. Mol. Spectrosc., 147, 91 2 = Demaison, J. & Rudolph, H. D. 1975, J. Mol. Struct., 24, 325 3 = Laurie, V. W. 1961, J. Chem. Phys., 34, 1516 4 = this study -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- Byte-by-byte Description of file: catalogue-file.txt -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1-11 F11.4 MHz Freq Predicted frequencies 13-18 F6.4 MHz Est(O-C) Estimated error 20-26 F7.4 nm^2MHz LGINT Base10 logarithm of the integrated intensity 28-28 I1 --- DR Degrees of freedom 30-39 F10.4 cm-1 ELO Lower state energy 41-43 I3 --- GUP Upper state degeneracy 45-49 I5 --- TAG CDMS entry tag 51-52 I2 --- J' Upper state J quantum number 54-55 I2 --- Ka' Upper state Ka quantum number 57-58 I2 --- Kc' Upper state Kc quantum number 60-60 I1 --- q (IS1) internal rotor components 62-63 I2 --- J" Lower state J quantum number 65-66 I2 --- Ka" Lower state Ka quantum number 68-69 I2 --- Kc" Lower state Kc quantum number 71-71 I1 --- q' (IS2) internal rotor components -------------------------------------------------------------------------------- Notes: 1. (IS1,IS2) are internal rotor components where 00 = A1A1, 01 = EE, 11 = A1E, 12 = EA1. 2. This format of the catalogue file is slightly different from CDMS format. References: 1. Groner, P. 1997, J. Chem. Phys., 107, 4483 2. Groner, P. 2012, J. Mol. Spectrosc., 278, 52 ================================================================================