1. In a 5- to 6-quart pan over high heat, bring 3 quarts water to a boil. Add pasta and stir occasionally until barely tender to bite, 9 to 12 minutes.
2. Meanwhile, in a 10- to 12-inch frying pan over high heat, stir onion in oil until limp, 3 to 5 minutes. Add tomatoes and juice, vermouth, broth, capers, and thyme. Bring to a boil and cook for 3 minutes. Add shrimp, reduce heat, and simmer, stirring occasionally, until barely opaque but still moist-looking in thickest part (cut to test), 3 to 4 minutes.
3. Drain pasta and return to 5- to 6-quart pan. Stir in shrimp mixture, parsley, and salt and pepper to taste. (If pasta has cooled, stir over medium heat until hot.) Pour into a wide serving bowl or distribute evenly among plates.