I want to create an interrupt service routine for the ADC interrupt that is caused by the ADCI flag when a conversion is finished. However, I can't find the interrupt vector to answer to said interrupt. How do I create the interrupt service routine?
I tried searching for the vector in the interrupt vector table (IVT) but it isn't specified there.
Unfortunately you did not specify the document you use. A quick web search revealed this family overview at Keil. The interrupt vectors are on page 45, and the vector for the ADC interrupt is 0x0053.
This means, your ISR starts at address 0x0053. With common C compilers the corresponding interrupt number is (0x0053 - 3) / 8 = 10.