Ground state rotational constants (in MHz), fitted to observed transitions at mass 78 u (C₆H₆) and 84 u (C₆D₆ or ¹³C₆H₆). Numbers in round brackets give the 1 − σ standard deviation in the corresponding last digits.

	C6H6	C6D6	13C6H6
B 0	5689.2855(54)	4707.3175(34)	5337.884(51)
D J	0.79(19) × 10−3	0.64(10) × 10−3	0.84(74) × 10−3
D JK	−0.78(51) × 10−3	−0.93(27) × 10−3	−4.1(23) × 10−3
D K	a[0.935 × 10−3]	a[0.536 × 10−3]	a[0.838 × 10−3]
H J	−5.1(20) × 10−6	−1.38(92) × 10−6
H JK	−8.1(91) × 10−6	−5.2(41) × 10−6
H KJ	55(17) × 10−6	0.221(74) × 10−6
Lines	16	18	16

^aValues from MP2 aug-cc-pVTZ calculation.