Spectrometer Using superconductor MIxer Receiver (SUMIRE) for Laboratory Submillimeter Spectroscopy

TL;DR

This paper introduces a novel laboratory spectrometer utilizing superconductor mixer receiver technology for precise molecular spectral line measurements in the submillimeter range, enhancing accuracy and sensitivity for astronomical applications.

Contribution

The development of a high-resolution, wide-band spectrometer with superconductor SIS receiver technology for laboratory molecular spectroscopy is presented as a new tool for accurate frequency measurements.

Findings

Frequency accuracy better than 1 kHz for strong lines

Successful spectral scan of CH₃OH from 216 to 264 GHz

Assignment of 242 CH₃OH transitions and 51 $^{13}$CH₃OH transitions

Abstract

Recent spectroscopic observations by sensitive radio telescopes require accurate molecular spectral line frequencies to identify molecular species in a forest of lines detected. To measure rest frequencies of molecular spectral lines in the laboratory, an emission-type millimeter and submillimeter-wave spectrometer utilizing state-of-the-art radio-astronomical technologies is developed. The spectrometer is equipped with a 200 cm glass cylinder cell, a two sideband (2SB) Superconductor-Insulator-Superconductor (SIS) receiver in the 230 GHz band, and wide-band auto-correlation digital spectrometers. By using the four 2.5 GHz digital spectrometers, a total instantaneous bandwidth of the 2SB SIS receiver of 8 GHz can be covered with a frequency resolution of 88.5 kHz. Spectroscopic measurements of CH$_3$CN and HDO are carried out in the 230 GHz band so as to examine frequency accuracy, stability, sensitivity, as well as intensity calibration accuracy of our system. As for the result of CH$_3$CN, we confirm that the frequency accuracy for lines detected with sufficient signal to noise ratio is better than 1 kHz, when the high resolution spectrometer having a channel resolution of 17.7 kHz is used. In addition, we demonstrate the capability of this system by spectral scan measurement of CH$_3$OH from 216 GHz to 264 GHz. We assign 242 transitions of CH$_3$OH, 51 transitions of $^{13}$CH$_3$OH, and 21 unidentified emission lines for 295 detected lines. Consequently, our spectrometer demonstrates sufficient sensitivity, spectral resolution, and frequency accuracy for in-situ experimental-based rest frequency measurements of spectral lines on various molecular species.