 One year later, the 3 − 2 transition at was observed in several regions, the clearest of which was the W3 IRS 5 cloud.The first far-IR 4 − 3 transition at 69.524 µm (4.3121 THz) was made in 1996 near Orion BN-IRc2.In 2001, three additional transitions of in were observed in the far infrared in Sgr B2; 2 − 1 transition at 100.577 µm (2.98073 THz), 1 − 1 at 181.054 µm (1.65582 THz) and 2 − 1 at 100.869 µm (2.9721 THz).