LABORATORY DETECTION OF HOCN AND TENTATIVE IDENTIFICATION IN Sgr B2

Abstract

The rotational spectrum of cyanic acid, HOCN, has been detected in the centimeter-wave band in a molecular beam by Fourier transform microwave spectroscopy and in the millimeter-wave band by conventional spectroscopy in a low-pressure laboratory discharge. Spectroscopic constants, including the nitrogen hyperfine coupling constant, derived from 31 a-type transitions between 21 and 360 GHz with J up to 17 and K a 2 allow the spectrum in the only rotational ladders populated in the interstellar gas to be calculated well into the submillimeter-wave band to 1 km s −1 or better in equivalent radial velocity. Four consecutive transitions of HOCN between 83.9 and 146.8 GHz were tentatively identified in published spectral line surveys of Sgr B2(OH). An approximate column density in Sgr B2(OH) of 6 × 10 12 cm −2 implies that the HOCN/ HNCO ratio is about 0.5%. Because HNCO is widely distributed in the interstellar gas, HOCN may be as well.

Interstellar HOCN in the Galactic center region

“…HOCN has previously been tentatively detected (Brünken et al 2009a) based on published spectral line survey data of Sgr B2(OH) obtained with the BTL 7 m and NRAO 11 m telescopes (Cummins et al 1986;Turner 1989). The current observations confirm and improve the detection of HOCN in several important ways: i) four unblended lines of HOCN were detected in the extended gas at an offset position (20 , 100 ) from the hot core Sgr B2(M) close to the maximum of HNCO emission.…”

“…The observed fairly constant abundance ratio of HOCN relative to HNCO in our sample of sources, which is far from thermodynamical equilibrium considering the low temperatures prevalent in the interstellar medium 2 , suggests that HOCN is formed along with HNCO on the grain mantles, and then subsequently released through shocks or during warm-up. Motivated by the recent detections of HCNO (Marcelino et al 2009) and HOCN (Brünken et al 2009a, and this work), E. Herbst and coworkers are currently extending the Ohio State gas-grain network to account for the formation and destruction of HNCO and its higher lying isomers in different types of sources (Quan et al, in preparation). Their hot core and warm envelope models can account reasonably well, i.e.…”

“…HNCO has also been detected in several external galaxies (Nguyen-Q-Rieu et al 1991;Wang et al 2004;Martín et al 2009), and been suggested as a tracer for nuclear starburst activity (Martín et al , 2009. Two energetically less stable isomers of HNCO have recently been detected in the interstellar medium: cyanic acid (HOCN) tentatively towards Sgr B2 (OH) following its laboratory identification (Brünken et al 2009a), and fulminic acid (HCNO) towards three starless dark clouds and one lowmass star-forming region (Marcelino et al 2009) with abundance ratios relative to HNCO of 0.5% and 1−5%, respectively. The relative abundances of members of an isomeric family reflect their different formation and destruction processes, and observations of isomers of small systems like HCN/HNC (e.g., Schilke et al 1992) as well as complex organic species (Hollis et al 2000;Turner & Apponi 2001) have been previously Based on observations with the IRAM 30-m telescope.…”

The puzzling behavior of HNCO isomers in molecular clouds

“…The reported HNCO/HOCN abundance ratio in the Galactic center (GC) clouds is between 40-400. Brünken et al (2009a) also obtained a tentative detection of HOCN in TMC-1 through the fundamental transition at 20.9 GHz. The derived column density is 7 × 10 10 cm −2 and the HNCO/HOCN abundance ratio is ∼100.…”

“…However, HCNO has not been detected toward the direction of the cyanopolyyne peak of TMC-1 or in the Orion Hot Core region. Cyanic acid (HOCN) is detected in several positions in the giant molecular cloud SgrB2 (Brünken et al 2009a(Brünken et al , 2010, after its characterization in the laboratory in the cm-and mmwave bands and a tentative detection in SgrB2(OH) based on previous spectral line surveys (Brünken et al 2009a). The reported HNCO/HOCN abundance ratio in the Galactic center (GC) clouds is between 40-400.…”