Left: spectra of H I, CO, OH 1612, OH 1665, OH 1667, and OH 1720 MHz (from top to bottom) toward the H I arc. The x-axis and y-axis denote the velocity in km s⁻¹ and the brightness temperature, respectively. Black dotted lines and velocity labels denote each of the velocity components in km s⁻¹ as seen in the OH 1667 MHz emission. The scaling factor of each spectrum is listed in the right panel of this figure. To avoid overlapping, the spectra of H I, CO, and OH have been shifted upwards by multiples of 5 K on the y-axis. Right: same as in the left panel but showing a zoom onto the spectra at the −74 km s⁻¹ component.