Fulcher-α band (d³Π_u- a³Σ_g⁺) spectra are widely used for the purpose of measuring rovibrational distribusion of the hydrogen molecules in divertor plasma in fusion devices, divertor plasma simulators and laboratory plasmas including negative ion sources. Since it has been known, from the early stage of the molecular spectroscopy, that the P and R branches originate in d³Π _u⁺ sublevel exhibit anomalous intensity compared to Q branch originate in d³Π _u^-[1], only the Q branch has been usually applied for the determination of the rovibrational distribution in the ground electronic state.
In this study, P, Q and R branches in the diagonal Fulcher-α transition are investigated using the hollow cathode glow discharge of 230 V - 70 mA. In the analysis, recently developed scheme including semi-classical excitation cross sections [2] and experimentally determined lifetime of the state involved are applied. Populations of the vibronic state v' ≥ 4 in the Q branch can be corrected to a considerable extent by taking into account the lifetime of the states, while those of any v' in the P and R branches cannot. Also, ratio of P and R branch intensities is far from that expected from the Hönl-London formula as well as that the rotational temperatures in the upper vibronic state d³Π _u⁺ is different from that in d³Π _u^-.
However, our initial results for 30 Pa discharge show that the average of the upper-Fulcher populations in the vibronic state deduced from the P and R branches coincide with those from Q branch by taking into consideration the difference in the selection rule of excitation from the ground electronic state based on the adiabatic approximation.
Different discharge conditions and plasma sources are compared to verify the observations, and mechanisms relating to the anomaly are discussed.

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