英语提问：麻烦分析一下这句话的结构,

英语提问：麻烦分析一下这句话的结构,
After the Ambassador had gone to investigate,a man called Horst aimed a fire extinguisher at him under the impression that the Ambassador was on fire.特别是under the impression .不是很明白,麻烦说详细点,

under the impression 原以为是这样的,以为
I was under the impression that you were coming tomorrow.
我以为你明天才来呢.
大使去调查后,一个名叫霍斯特把灭火器对准了他,他以为这位大使着火了.
再问： under the impression that the Ambassador was on fire.在整个句子中充当什么成分？
再答： 状语，表示伴随