We present 12 mm Mopra observations of the dense ( > 10 ^ { 3 } cm ^ { -3 } ) molecular gas towards the north-east ( NE ) of the W28 supernova remnant ( SNR ) .
This cloud is spatially well-matched to the TeV gamma-ray source HESS J1801 - 233 and is known to be a SNR-molecular cloud interaction region .
Shock-disruption is evident from broad NH _ { 3 } ( 1,1 ) spectral line-widths in regions towards the W28 SNR , while strong detections of spatially-extended NH _ { 3 } ( 3,3 ) , NH _ { 3 } ( 4,4 ) and NH _ { 3 } ( 6,6 ) inversion emission towards the cloud strengthen the case for the existence of high temperatures within the cloud .
Velocity dispersion measurements and NH _ { 3 } ( n , n ) / ( 1,1 ) ratio maps , where n=2 , 3 , 4 and 6 , indicate that the source of disruption is from the side of the cloud nearest to the W28 SNR , suggesting that it is the source of cloud-disruption .
Towards part of the cloud , the ratio of ortho to para-NH _ { 3 } is observed to exceed 2 , suggesting gas-phase NH _ { 3 } enrichment due to NH _ { 3 } liberation from dust grain mantles .
The measured NH _ { 3 } abundance with respect to H _ { 2 } is \sim ( 1.2 \pm 0.5 ) \times 10 ^ { -9 } , which is not high , as might be expected for a hot , dense molecular cloud enriched by sublimated grain-surface molecules .
The results are suggestive of NH _ { 3 } sublimation and destruction in this molecular cloud , which is likely to be interacting with the W28 SNR shock .