Laboratory Measurement of CH2DOH Line Intensities in the Millimeter-wave Region

Abstract

Deuterium fractionation in molecules is known as one of the most powerful tools to study chemical processes during star and planet formation. Among various interstellar molecules, methanol often shows very high deuterium fractionation. It is the most abundant saturated organic molecule and is known as a parent species to form more complex organic molecules. However, deriving the abundance of deuterated methanol suffers from the uncertainty in the intrinsic line intensities ( S μ ^2 ) of CH _3 OH isotopologues. Due to their floppy nature, theoretical evaluation of the S μ ^2 values is not straightforward, particularly for asymmetric-top asymmetric-frame isotopologues such as CH _2 DOH. In this study, we have measured the line frequencies and their intensities for CH _2 DOH in the millimeter-wave region from 216 to 264 GHz by using an emission-type millimeter and submillimeter-wave spectrometer. For the a -type J = 5 − 4 transition, the derived S μ ^2 values are 13%–27% larger than those theoretically calculated, except for the transitions of K _a = 2 for e _0 and K _a = 1 for e _1 affected by avoided level crossing. For b -type transitions, significant systematic differences are found between theoretical and experimental S μ ^2 values. The results of the present study enable us to accurately derive from observations the CH _2 DOH abundances, which are essential for understanding deuterium fractionation in various sources.

Keywords

• Molecular spectroscopy
• Line positions
• Line intensities
• Astrochemistry